'Sr' (ii) was the Japanese seizure of Lae and Salamaua on the south-eastern end of North-East New Guineas coast (8/10 March 1942).

The military value of the eastern half of New Guinea to the Japanese was as a barrier to protect the Japanese forces' southern flank, a base from which Australia could be threatened, and a position from which to block the Torres Strait in order to cut communication between the South Pacific and the Netherlands East Indies as well as the Indian Ocean. This last would compel the naval and merchant shipping of Japan’s opponents to detour around the south coast of Australia.

The day after the Japanese had landed in Sarawak in 'B' (ii) during the middle of December 1941, the evacuation of all European women and children from New Guinea and Papua was ordered on 17 December 1941. The Japanese bombed Lae, Salamaua and Madang on 21 January 1942, forcing the abandonment of the first two, as part of their 'R' operation in which they occupied Rabaul, on the island of New Britain, two days later.

It was March 1942 before the Japanese were within sight of completing their campaign to take the Netherlands East Indies and started to consider whether to consolidate along their current strategic perimeter or seek to expand this to the south and east. The significance of the huge island continent of Australia as a base for a future Allied counter-offensive was evident to each side, and the Japanese began preparations to cut the sea lanes between Australia and the western seaboard of the USA. The Japanese planned to secure eastern New Guinea, including strategic Port Moresby, in 'Mo' before advancing to the south-east in 'Fs' toward the Fiji and Samoa island groups.

Foreseeing this move, on 26 February Admiral Ernest J. King, the US Chief of Naval Operations, ordered Admiral Chester W. Nimitz, commander of the US Pacific Fleet and heading the Pacific Ocean Areas command, to keep some of his aircraft carrier strength in the ANZAC area to guard against any such Japanese expansion. On 2 March King sent additional orders for Vice Admiral Herbert F. Leary, commanding ANZAC, and Vice Admiral Wilson Brown, commanding Task Force 11 1, to attack Rabaul on or about 10 March. Four days later Rear Admiral Frank J. Fletcher’s TF17 (fleet carrier Yorktown and destroyers Russell and Walke) had joined TF11 in the Coral Sea.

In the aftermath of the Japanese 'Ai' attack on Pearl Harbor, the US Navy had taken urgent steps to reinforce the Pacific Fleet. The fleet carrier Yorktown passed through the Panama Canal at the beginning of January 1942, and on 6 January departed San Diego on her first mission, as the core of TF17 escorting the 'Picador' (ii) garrison troop convoy to Samoa, which was reached on 20 January. This convoy comprised the transports Jupiter, Lassen, Lurline, Matsonia and Monterey, and delivered the 2^nd Marine Brigade to Pago Pago in the Samoan islands group. The fleet carrier Enterprise departed Pearl Harbor in the Hawaiian islands group as the core of TF8 a few days later and headed to the south to make rendezvous with the convoy.

While this precautionary move was under way, the Pacific Fleet suffered its first carrier casualty. The fleet carrier Saratoga, which was patrolling to the south-west of Oahu island as the core of TF14, was torpedoed on 11 January by the submarine I-6: three of the carrier’s engine rooms were flooded, but Saratoga nonetheless managed to return to Pearl Harbor under her own steam. After emergency repairs she was despatched to the Bremerton Navy Yard, Washington, for repair and a refit. Saratoga was replaced in the Pacific Fleet by Hornet, like Yorktown a sister ship of Enterprise.

The deployment of these carriers to the South Pacific had a dual purpose. Once their escort task had been completed, they departed Samoa on 25 January and steamed to a position from which attacks could be launched on the Japanese positions in the Gilbert island and Marshall island groups: these were of great importance as the first direct offensive undertakings by the Pacific Fleet’s carrier force.

The operation involved the use of three carrier task forces, two to make the attacks while the third, TF11 with Lexington, provided distant cover from a position to the east of Wake island. TF8 was commanded by Vice Admiral William F. Halsey and comprised Enterprise, three cruisers and six destroyers: the targets for air attack were airfields and shipping in the Marshall islands group, while the cruisers undertook gunfire bombardments of shore installations on Taroa island. Under the command of Fletcher, who had been transferred after Saratoga's return to Pearl Harbor following the Wake island relief undertaking, TF17 was centred on Yorktown, and had a strength similar to that of TF8. The two attack forces were some 500 miles (800 km) apart and the only co-ordination between them was the timing.

Task Group 8.5 of TF8 was barely 40 miles (65 km) from the nearest Japanese base, Wotje atoll, when the first attack, delivered by 37 Douglas SBD Dauntless dive-bombers and nine Douglas TBD Devastator level bombers, was launched early in the morning of 1 February against Kwajalein atoll. The aircraft took off from Enterprise, which was escorted only by the destroyers Blue, McCall and Ralph Talbot, and formed in the dark, the plan being that they would be over their targets, some 155 miles (250 km) distant, at dawn. All the dive-bombers were briefed to strike at the airfield on Roi island, at the northern end of the atoll, leaving the shipping off Kwajalein island, at the southern end, to the level bombers, each carrying three 500-lb (227-kg) bombs rather than a single torpedo, to allow the engagement of alternative targets in the absence of shipping.

The Roi attack force became divided, and 10 of its SBD dive-bombers joined the TBD bombers on their way to Kwajalein, and the remainder lost all surprise as a result of the age of their charts, which were inaccurate and did not show the airfield. Japanese fighters were therefore able to effect an interception and four of the dive-bombers were lost, apparently to Mitsubishi A5M 'Claude' fighters; in return the US aircraft claimed three fighters shot down. The Kwajalein attack located a mass of targets as the lagoon was full of small warships and merchant vessels, but in this and an attack by the nine level bombers, some three hours later, no direct hits were scored and only near-miss damage was inflicted on the light cruiser Katori, minelayer Tokiwa and five smaller warships and auxiliaries. One small auxiliary gunboat later sank. No fighters interfered and the SBD and TBD warplanes returned the carrier without loss.

Enterprise's fighters had provided no escort: each armed with two 100-lb (45-kg) bombs, five had been sent to Maleolap island, and another six bomb-armed aircraft Wotje island. The Maleolap attack destroyed two aircraft on the ground.

Under the command of Rear Admiral Raymond A. Spruance, TG8.1 comprised the heavy cruisers Northampton and Salt Lake City and the destroyer Dunlap, and this undertook the gunfire bombardment of Wotje atoll. Under the command of Captain Thomas M. Shock, TG8.3 comprised the heavy cruiser Chester and destroyers Balch and Maury, and undertook a similar bombardment of Taroa island in the Maloelap atoll group, Chester receiving slight damage after coming under air attack and suffering near-misses by many small bombs and being hit by one small bomb. The bombardment was followed by an attack by nine unescorted SBD dive-bombers, and these were severely handled by A5M fighters, which claimed three US aircraft for the loss of one of their own machines. The F4F fighters despatched to Wotje island found no airfields but a quantity of shipping, which they attacked and claimed to have damaged: though several ships were indeed hit, the light bombs delivered by the US warplanes caused only the most superficial of damage.

The Japanese did not locate TF8 until it had started to withdraw, some nine hours after the first launch. Seven Japanese aircraft attacked, and six were shot down by anti-aircraft fire and fighters: one Mitsubishi G4M 'Betty' bomber attempted to crash on the carrier. however, but misjudged its approach and merely clipped the edge of the flight deck.

Escorted by the heavy cruiser Louisville, light cruiser St Louis and destroyers Hughes, Mahan, Russell, Sims and Walke, the carrier Yorktown also launched her aircraft before first light, sending 11 TBD and 17 SBD warplanes against Jaluit island, which had been intended as the target for an attack by Lexington's aircraft in December 1941 before being cancelled. The US aircraft attacked at dawn, out of a thunderstorm, and although they caused a small amount of damage to shore installations, only two small ships suffered any damage, while six of the SBD machines were lost, two of them to the weather and the other four to anti-aircraft fire. Makin island, in purist terms the only member of the Gilbert island group to be attacked, was struck by nine SBD dive-bombers, which inflicted slight damage on one small naval auxiliary, and Mili atoll, which was thought to be a seaplane base, was found to have no military installations obvious from the air.

TF17 thus accomplished little apart from costly crew training in the nature of modern carrierborne air warfare: four aircraft had been shot down and three lost to the weather conditions. TF17 then withdrew without molestation except for a single Kawanishi H6K 'Mavis' reconnaissance bomber flying boat which tried to bomb a screening destroyer, missed, and was shot down by a fighter of the VF-5 squadron as the first known victory by a US carrierborne fighter.

After this, Enterprise returned to Pearl Harbor and Yorktown headed for the South Pacific, where she and Lexington were to operate against any Japanese attempt to overrun New Guinea or penetrate into the Coral Sea, thereby threatening Australia.

At the beginning of March, in response to the orders of Nimitz and Halsey, Brown planned to have the aircraft of one of his carriers attack Rabaul and those of the other strike at Gasmata, then bombard both bases with surface warships detached from the task forces. Rear Admiral J. G. Crace, the British officer commanding the Australian naval forces, was eager to see some action and welcomed his bombardment mission against Gasmata, but Rear Admiral William W. Smith, commanding the escort for TF17, was strongly opposed to the prospect of taking his cruisers up the St George Channel to Rabaul with no guarantee of air cover and the distinct possibility of encountering a superior Japanese cruiser force when he got there.

Lae was bombed by the Japanese on 21 January 1942 in preparation for their 'R' move against Rabaul two days later. As a result of the bombing, the town was largely abandoned.

Some 30 miles (50 km) inland from the north coast of North-East New Guinea, Wau was bombed by the Japanese on 1 February. The only defence capability on the north coast, in the form of a few hundred men of the New Guinea Volunteer Reserve, was located there. The only other Allied unit on the mainland was a reinforced Australian battalion at Port Moresby, but reinforcement soon arrived in the form of Brigadier Selwyn H. W. C. Porter’s Australian 30^th Brigade. On 3 March the Japanese flew their first air raid against a target on the Australian mainland, bombing Wyndham in the northern part of Western Australia.

Meanwhile Vice Admiral Shigeyoshi Inoue, commander of the 4^th Fleet, was preparing 'Sr' (ii) to seize the area of Lae and Salamaua, including the airstrip at Lae from which the Japanese could project air power forward to Port Moresby. On 5 March Rear Admiral Sadamichi Kajioka departed Rabaul with the 'Sr' Invasion Force 2. The five transport vessels carried the 2/144^th Regiment of Major General Tomitaro Horii’s South Seas Detachment in the 6,469-ton Yokohama Maru and 5,870-ton China Maru, and the 2^nd Maizuru Special Naval Landing Force in the 8,624-ton Kongo Maru, 6,843-ton Tenyo Maru and 3,871-ton Kokai Maru. Warship cover was provided by Rear Admiral Aritomo Goto’s Support Force with the heavy cruisers Aoba, Furutaka, Kako and Kinugasa of the 6^th Cruiser Squadron, the light cruisers Tatsuta and Tenryu of the 18^th Cruiser Squadron, and three destroyers. Air cover was provided by 15 Mitsubishi A6M Reisen 'Zero' fighters, 21 G4M 'Betty' bombers, and six Kawanishi H6K 'Mavis' flying boats from Rabaul. Another 19 A6M fighters were to be delivered by the light carrier Shoho on 9 March, and more of these fighters were scheduled to stage through Gasmata to the airstrip at Lae once it had been taken.

On 6 March 1942 Brown’s ships were was refuelling in readiness for the dash to their launch point for the planned air attacks. At this juncture there began to arrive intelligence reports of a Japanese move to the west from New Britain. Brown disregarded the intelligence until just before 24.00 on 7/8 March, when he received more precise intelligence of a Japanese convoy 150 miles (240 km) to the south-west of Gasmata and making for the area of Lae. As the convoy offered a tempting target far from Japanese air cover, Brown immediately abandoned the planned raid on Rabaul and prepared to attack the Japanese convoy when it reached Lae. Lae was a difficult target, however, for the approach from the east would require Brown’s force to steam through an area which had been well reconnoitred by the Japanese to avoid the poorly charted reefs of the Louisiade islands group off the south-eastern tip of New Guinea.

A better solution was identified by Captain Frederick C. Sherman, captain of Lexington, who discovered that the Gulf of Papua to the west of Port Moresby was within comfortable flying distance of Lae. There were no good charts of New Guinea, though, and it was rumoured that the mountains of the Owen Stanley range reached to a height of 15,000 ft (4570 m) or more, too high for heavily laden torpedo bombers. The commander of Lexington's embarked air group, Lieutenant Command William B. Ault, flew to Port Moresby and learned that there was a pass, at a height of 7,500 ft (2285 m), through the mountains almost directly along the projected route and that the weather was usually favourable at a time early in the morning.

It was discovered on 8 March that the Japanese transport ships had arrived off Salamaua, and Brown had his ships in position to launch air attacks by dawn on 10 March. To increase the size of the US air attack force, Sherman launched his fighters first, then his attack aircraft, and then quickly recovered and refuelled the fighters to be relaunched and join the attack aircraft as escorts. A total of 18 F4F Wildcat fighters, 61 SBD Dauntless dive-bombers, and 25 TBD Devastator torpedo bombers was despatched. In the attack which resulted, the US pilots claimed to have inflicted extensive damage, including five transports, three cruisers and one destroyer sunk, one minelayer and two more destroyers probably sunk, and one seaplane tender badly damaged. Fletcher’s combat intelligence officer failed to confirm Japanese losses of this magnitude, but Brown refused to launch a second attack, citing the damage already inflicted and a deterioration of the weather over the mountain pass. The actual damage inflicted by the US air attack was two transports (Kongo Maru, Yokohama Maru) and one minelayer sunk, and two transport vessels (including Tenryu Maru, which was beached to prevent her from sinking), light cruiser Yubari, seaplane tender Kiyokawa Maru, minelayer Tsugaru and destroyers Asanagi and Yunagi damaged. Some 350 men were killed on the transport vessels.

This was a significant loss to the 4^th Fleet, though the transports had in fact already all but completed unloading, and the occupation of Lae and Salamaua by the 2^nd Maizuru Special Naval Landing Force and the battalion of the 144^th Regiment had been completed by 01.00 and 02.00 respectively. In the short term, however, Inoue called off the planned occupation of Port Moresby until carrier support could be provided by Admiral Isoroku Yamamoto’s Combined Fleet.

The Japanese desired Salamaua and Lae as advanced air bases for the bombing campaign they planned against Port Moresby, the primary Allied base area in Papua, and Japanese engineers had Lae airstrip ready to receive aircraft within 36 hours of the landing.

The main Japanese bases in the theatre were located around Rabaul in New Britain, some 550 miles (885 km) to the north, and though both bombers and escorting fighters could operate over this considerable radius, the lengthy operational radius nonetheless forced a reduction in the bombers' loads and in the fighters' loiter times over the target area. The region around Lae offered good sites for advanced air bases, with Salamaua offering defensive positions against any Allied counterattack from the south and west, the more so as most of the civilians in the area had fled in the bombing that preceded the Japanese capture of Rabaul and Kavieng.

The Japanese took Finschhafen, to the north-east at the tip of the Huon peninsula, two days later, and by this time the army troops had been re-embarked, leaving the naval engineers and marines to establish the necessary communications facilities and air bases. The Japanese were soon in full control of the Huon peninsula.

'Sr' (ii) was just part of the Japanese extension to the south-east, where the Imperial General Headquarters wished to establish a powerful strategic barrier against any Allied counter-offensive into the Bismarck Sea. Further Japanese advances during March included the occupation (followed by airfield construction) of Buka, Bougainville and the Shortland islands group at the north-western end of the Solomons islands chain, of Manus island in the Admiralty islands group, and of Halmahera island between the western tip of New Guinea and Mindanao island in the south of the Philippine islands group. Thus Rabaul, the key to Japan’s defence of her south-eastern perimeter, was hedged about defensively by naval and air bases on Japanese-held islands.

The Shortland islands group is located just off the southern tip of Bougainville at the head of what soon came to be known as 'The Slot'. Shortland island itself is about 13 miles (21 km) long and 10 miles (16 km) wide, relatively flat with a maximum elevation of 777 ft (237 m) and heavily forested. Most of the coast is fringed by coral reefs, and the nearby small islands are covered with palms.

The Japanese occupied the island in the course of 13 March, and its anchorage became an important staging area for Japanese forces heading down 'The Slot' toward Guadalcanal. The Japanese also established a seaplane base at the small neighbouring islet of Faisi and an airfield on Ballale islet. Faisi eventually became the headquarters of the 8^th Fleet and was garrisoned by the 5,000-man 1^st Base Force. Ballale airfield was constructed by the 18^th Construction Battalion between November 1942 and January 1943. Lacking bulldozers, the Japanese used some 517 British prisoners of war, primarily artillerymen taken prisoner at Singapore. The Japanese refused the prisoners of war permission to build any kind of air raid shelters, and most of the artillerymen were eventually killed either in air raids or as a result of Japanese abuse, and their last survivors were allegedly massacred on 5 March 1943.

The Admiralty islands group comprises about 20 volcanic islands, with a total land area of about 800 sq miles (2020 km²), just to the north of the eastern end of New Guinea. The islands are rugged and covered with jungle. Most of the coasts are fringed with coral reefs, leaving only a few small beaches suitable for landing operations. The largest island of the group is Manus, which is 49 miles (70 km) long and 16 miles (26 km) wide with central mountains reaching to a height of 2,355 ft (718 m). To the north-east of Manus is a superb anchorage, Seeadler Harbour, which is 15 miles (24 km) long and 4 miles (6.4 km) wide, and this was a major strategic value in the South Pacific campaign. The island’s main settlement was Lorengau, to the south of Seeadler Harbour. In 1939 there were only 44 Westerners, mostly plantation managers, living in the island group, and the indigenous population numbered about 13,000. The islands were completely undeveloped, with no roads outside the immediate vicinity of Lorengau. A native trail ran along the north coast of Manus, and three trails crossed the interior mountains to the south coast.

The Japanese bombed Lorengau on 21 January 1942, occupied Manus on 8 April 1942 using the 51^st Transport Regiment of the 51^st Division, and completed a 4,020-ft (1225-m) airstrip at Momote on the island of Los Negros, to the east of Seeadler Harbour. In 1943 they completed a 3,280-ft (1000-m) airstrip to the north-west of Lorengau. At the same time the garrison was reinforced with elements of the 14^th Base Force and single battalions of the 1^st Independent Mixed Regiment and the 229^th Regiment. The garrison remained relatively small, numbering about 4,600 men.

Halmahera (also known as Jilolo) is located between Celebes island and New Guinea, and is the largest of the Molucca (Spice) islands group. It is about 200 miles (320 km) in length from north to south and 90 miles (140 km) in width from east to west with an area of more than 7,000 sq miles (18130 km²). The island is mountainous with its peak at 5,364 ft (1635 m) at Mt Gamkonora near its centre.

The island was occupied by the Japanese in 1942 and there were nine airfields completed or under construction by a time late in 1944. The garrison numbered some 37,000 men, and in combination with terrain including strong natural defences, persuaded the Americans that it would be too costly to take, and they instead opted to take Morotai island, just to the north, in 'Tradewind' on 15 September 1944.

Thus Rabaul, the key to Japan’s defence of her south-eastern perimeter, was as noted above hedged about defensively by naval and air based on Japanese-held islands.