'Cactus' (i) was the US sub-plan within 'Watchtower' concerned specifically with the capture of the area round Lunga Point on Guadalcanal in the Solomon islands group (7 August 1942).

The codename also led to the use of the phrase Cactus Air Force for all the Allied air elements assigned to the island of Guadalcanal from August 1942 until December 1942 during the main phase of the Guadalcanal campaign, and most especially to those units operating from Henderson Field. After December, as the campaign entered in final phase, the official name of the air units became Commander, Aircraft, Solomons (AirSols), but the phrase Cactus Air Force remained in general use until April 1943, when the designation Aircraft, Solomons (also AirSols) was standardised.

In committing their country to full participation on the Axis side in World War II from 7/8 December 1941, the political and military leaders of Japan sought initially to neutralise the US Pacific Fleet and US strength in the Philippine islands group, seize British and Dutch territories rich in natural resources, and obtain strategic military positions with which to defend their increasingly far-flung empire. Within this overall concept, therefore, Japanese forces also attacked or took Hong Kong, Thailand, Malaya, Singapore, the Dutch East Indies, and other islands or island groups such as Wake, New Britain and New Ireland, and Guam. The Japanese then decided to extend their defensive perimeter to the south and south-east, and while these efforts were partially successful in land, they failed in operational and strategic terms as a result of the US Navy’s strategic victories in the 'Battle of the Coral Sea' during May 1942 as a consequence of 'Mo' (ii) and the 'Battle of Midway' during June 1941 as a consequence of 'Mi' (ii).

These two US victories gave the Allies the opportunity to take the initiative and launch a counter-offensive against the Japanese somewhere in the Pacific. The location which the Allies chose was the Solomon islands group, and more specifically the islands of Guadalcanal, Tulagi and Florida at the group’s south-eastern end. The Allies knew that the Japanese navy had occupied Tulagi in May 1942 and had constructed a seaplane base, thereby extending the range of the Japanese reconnaissance capability, and the level of Allied concern began to grow from a time early in July of the same year when it became clear that the Japanese navy had embarked on the construction of a significant airfield near Lunga Point on nearby Guadalcanal island, from which long-range bombers might be able to interdict the Allied maritime lines of communication between the western USA and Australasia. When complete, the Allies appreciated, these bases would protect Japan’s major base at Rabaul, threaten Allied supply and communication lines across the South Pacific to Australia and New Zealand, and establish a staging base for possible future offensives against the New Hebrides, Fiji, Samoa and New Caledonia.

The Allied plan to attack the Japanese positions in the south-eastern part of the Solomon islands group was conceived by Admiral Ernest J. King, the commander-in-chief of the US Fleet. King proposed the counter-offensive firstly to deny the Japanese the use of the south-eastern Solomon islands, and secondly to allow their use by the Allies as the starting point for a campaign to isolate the major Japanese base at Rabaul in New Britain and also for the support the Allied campaign in New Guinea. Admiral Chester W. Nimitz, commander-in-chief of the Pacific Ocean Areas command, created the South Pacific theatre of operations with Vice Admiral Robert L. Ghormley at its head from 19 June to control the Allied offensive in the Solomon islands.

On 7 August Major General Alexander A. Vandegrift’s US 1^st Marine Division landed on Tulagi and also at Lunga Point on Guadalcanal, capturing the partially completed Japanese airfield and marking the start of the first Allied counter-offensive of the Pacific War. The Americans immediately continued the construction of the airfield, using captured Japanese equipment for the most part. On 12 August the airfield was named Henderson Field in honour of Major Lofton R. Henderson, who had been killed during the 'Battle of Midway' and the first marine pilot killed in that the battle. By 18 August, Henderson Field was ready for use.

When the first aircraft began to arrive, Henderson Field was still more of an airstrip than a real airfield, for it was an irregularly shaped area hacked out of the island’s vegetation and with about half of its area based on a cleared part of a coconut plantation. The runway was too short, and there were only a few revetments to protect the aircraft from the fragments of exploding artillery shells and bombs, and from strafing attacks by Japanese aircraft. After landing on 4 September, Colonel W. Fiske Marshall, the commander of Marine Aircraft Group 25, described the airfield as something out of 'a Doré drawing of hell'.

Aligned on a north-west/south-east axis, the runway had a gravel surface 2,400 ft (730 m) long extended by 1,000 ft (305 m) of matting, and was often pitted by the craters of incoming Japanese artillery and naval gun fire. The runway was so poor, indeed, that it caused as many aircraft losses as Japanese action. In the humid heat typical of Guadalcanal, when dry the airfield’s air was permeated with black dust which fouled the warplanes' engines, and when wet the airfield soon became sodden, with runway operations then covering aircraft with glutinous muck. The runway was lengthened and widened several times during the Guadalcanal campaign, and by 4 September was 3,800 ft (1160 m) long and 150 ft (46 m) wide.

Henderson Field was very close to the US perimeter round Lunga Point, and as a result security was a constant concern as the Japanese had a well earned reputation as clever nocturnal infiltrators. Other problems faced by the Americans were a total lack of fuel bowsers, hangars and covered repair facilities. Damaged aircraft were frequently cannibalised for spare parts, and as there were no bomb hoists all munitions had to be hand-loaded onto the warplanes. Fuel was always in very short supply, and had to be hand-pumped from 55 US gal (45.8 Imp gal; 208.2 litre) drums. Fuel bowsers were later delivered, but the fuel still had to be hand-pumped into these.

On 9 September, the 6^th Naval Construction Battalion ('Seabees') completed a second runway about 1 mile (1.6 km) to the east of Henderson Field’s original runway. This 'Fighter 1' runway was built of tamped-down sod, and was about 4,600 ft (1400 m) long and 300 ft (91 m) wide. The marine fighter squadrons began to operate from Fighter 1, and other units continued at Henderson Field’s original runway, which became 'Bomber Field No. 1'.

An improvement of Henderson Field’s facilities began in the middle of November, when Henderson Field became an official marine corps air base. Local coral was too rotten and soft for airfield use, so ground coral was shipped in to allow the creation of proper runways.

Living conditions on Guadalcanal can most charitably be described as difficult. Pilots and ground crew lived in mud-floored tents in 'Mosquito Grove', which was a flooded coconut plantation, and at one time or other most marines were stricken down by tropical diseases such as malaria, dysentery and dengue fever, and fungal infections were rife. Japanese warships made periodic nocturnal bombardment of the airfield, and Japanese artillery attacks were frequent. The worst night of bombardment was 13/14 October, when two Japanese battleships fired more than 700 rounds of main armament projectiles onto Henderson Field to provide cover for the landing of troops farther to the west. The misery of those on the ground was completed, at about 12.00 on most days, by the arrival of some 20 to 40 Mitsubishi G4M 'Betty' twin-engined medium bombers, which cruised in formation over the airfield and bombed from an altitude of about 19,685 ft (6000 m). The bombers were always escorted Mitsubishi A6M Reisen 'Zero' single-engined fighters.

Between 20 August, when the first marine squadron landed, and 25 August there was no commanding officer for the marine air unit, which thus reported directly to Vandegrift. This reflected the fact that the US Marine Corps had not designated an air operations commander, but the US Army Air Forces already had a squadron present, and the field had already developed something of the feeling of a US Navy base after having been promised to certain naval units. The first marine commander was Colonel William W. Wallace, but he only retained command temporarily.

The Cactus Air Force came technically under the command of Rear Admiral John S. McCain, commander of all land-based Allied air units in the South Pacific Area. Vandegrift and his operational commanders, however, exercised local command over the Allied aircraft operating out of Henderson Field.

Matters began to change for the better on 3 September with the arrival of Brigadier General Roy S. Geiger on board a Douglas R4D transport that was the first aeroplane of the South Pacific Combat Air Transport Command to land on the island. As the 'Commander, Aircraft, Guadalcanal' (ComAirCACTUS) and the 1^st Marine Aircraft Wing, Geiger established his headquarters in a wooden Japanese pagoda located on a hill about 200 yards (180 m) from the airfield. Geiger set about improving the capabilities and the morale of the air personnel at Henderson Field, and achieved much before mental and physical exhaustion compelled his to hand over to his chief-of-staff, Brigadier General Louis E. Woods, on 7 November. It was Woods who led the Cactus Air Force during what was generally seen as the lowest point of the US campaign. But Woods was the right man for the task, and it was a more capable air unit which Woods passed on to his successor, Brigadier General Francis P. Mulcahy, commander of the 2^nd Marine Aircraft Wing, on 26 December.

Most of the Japanese warplanes against which the Cactus Air Force fought were of naval air units. On 7 August, when the Guadalcanal campaign began, the Rear Admiral Sadayoshi Yamada’s 5^th Air Attack Force was based at Rabaul on New Britain and at Lae in North-East New Guinea, and was responsible for naval air operations over the eastern part of New Guinea and the Solomon islands group. The 5^th Air Attack Force was a hybrid unit comprising mainly attached units from the 25^th Air Flotilla and reporting to Vice Admiral Nishizo Tsukahara’s 11^th Air Fleet.

On 7 August the 5^th Air Attack Force had 39 fighters, 32 medium bombers, 16 dive-bombers, and 17 seaplanes, the last including the 15 seaplanes based at Tulagi and destroyed in the initial Allied air attacks during the 'Ringbolt' landing on Tulagi and 'Watchtower' landing on Guadalcanal. The 5^th Air Attack Force's principal bomber unit was the 4^th Air Group equipped with the G4M 'Betty', and 24 of its fighters belonged to Captain Masahisa Saito’s 'Tainan' Air Group. This latter had on strength some of the ablest Japanese fighter aces and flew the A6M2 'Zero' fighter. With 55 pilots and 24 aircraft, only the most experienced and able pilots of the 'Tainan' Air Group were allowed to consistently participate in combat operations. The Aichi D3A1 'Val' single-engined dive-bombers and the rest of the fighters, of the A6M3 variant, belonged to the the 2^nd Air Group. Most of the dive-bombers were lost during the attacks of 7 and 8 August on the Allied landing forces. On these two days the 'Misawa' Air Group of Vice Admiral Seigo Yamagata’s 6^th Air Attack Force (otherwise the 26^th Air Flotilla from Tinian in the Mariana islands group flew 27 G4M bombers to supplement the 5^th Air Attack Force at Rabaul. Around the same time Tsukahara moved from Tinian to Rabaul to undertake more direct control of air operations against Allied forces in the Guadalcanal area.

The 4^th Air Group and 'Misawa' Air Group suffered heavy losses during their attacks on the Allied landing fleets off Guadalcanal on 7 and 8 August, losing 24 bombers and 153 airmen killed, while the Tainan Air Group lost four A6M fighters and four pilots. Until replacement and reinforcements arrive, the 5^th Air Attack Force could not continue its attacks on the marine positions on Guadalcanal, a fact which provided the US forces the uninterrupted time they needed to ready the captured airfield at Lunga Point for the arrival of US warplanes. On 20 August, 19 G4M bombers of the Kisarazu Air Group of the 6^th Air Attack Force arrived at Kavieng on New Ireland, to the north of New Britain. On 2 September, 10 G4M bombers of the Chitose Air Group of the 24^th Air Flotilla also arrived at Kavieng. Both groups were involved in subsequent bombing raids on Guadalcanal. Some 13 A6M fighters and pilots of the 6^th Air Group joined the 2^nd Air Group at Rabaul on 31 August 31 and started to participate in combat missions over Guadalcanal on 11 September.

From 1 October to the end of the war, the 11^th Air Fleet was commanded by Vice Admiral Jinichi Kusaka, who also had his headquarters at Rabaul.

A Japanese seaplane force was created on 28 August as the R-Area Air Force under the command of Rear Admiral Takatsugu Jojima, and this operated from Rabaul as well as forward operating bases at Buin on Bougainville island, in the Shortland Islands, and at Rekata Bay on Santa Isabel island. The aircraft operated by the R-Area Air Force came from the four squadrons assigned to the Japanese seaplane tenders Kamikawa Maru, Chitose, Sanyo Maru and Sanuki Maru. The primary task of the R-Area Air Force was the provision of air cover for convoys carrying troops, equipment and supplies to Guadalcanal, but the unit also undertook reconnaissance missions around the area of the Solomon islands group, and occasionally attacked Henderson Field.

Finally, air units from Admiral Isoroku Yamamoto’s Combined Fleet aircraft carriers, including Shokaku, Junyo, Zuikaku and Ryujo, operating from either land bases with the 11^th Air Fleet, or from the carriers themselves, engaged the aircraft of the Cactus Air Force at various times during the Guadalcanal campaign.

Fighter pilots of the US Navy and US Marine Corps, who had at first little experience with high-altitude flight and combat, were initially at a disadvantage as their Grumman F4F Wildcat single-engined fighter was not in the same class as the A6M in terms of ceiling, climb rate and manoeuvrability. The A6M was lighter and faster and possessed a superior climb rate. The US pilots soon learned not to enter dogfighting combat with the A6M, but instead deliver one burst of fire as they dived at high speed past the target before regrouping, climbing and attacking once again. The pilots of the Cactus Air Force constantly refined their tactics and techniques, and swiftly learned to improve their gunnery and to place a strong reliance on team work in which pairs of aircraft collaborated to provide mutual support.

Even so, the F4F had some positive features in combat against the A6M inasmuch as its was more stronger built, had better defensive armour and self-sealing fuel tankage, and possessed good firepower in its six 0.5-in (12.7-mm) Browning M2 machine guns.

Given that they could not dogfight effectively against the Japanese fighter, the US fighter pilots quickly came to appreciate that their best tactic was to break the cohesion of any raid and live to fight another day. Thus the primary targets of the US fighters pilots was not the Japanese fighters, against which they were at a disadvantage and which had little power to inflict damage to forces in the ground, but the bombers. The leading light in the development of what became very effective US tactics was Major John L. Smith, and as a result US fighters always tried to secure an altitude advantage of 5,000 ft (1525 m) or more before committing themselves to the attack, in which concentrated their efforts on the Japanese aircraft at the back of any formation. This provided them with good firing angles against the unprotected fuel tanks of the Japanese bombers, and also made the fighters poor targets for the bombers' gunners. Moreover, the US tactic demanded that the escorting Japanese fighters had to climb as rapidly as they could to try to intercept the US fighters, thereby burning more fuel than planned and reducing their endurance over Guadalcanal.

Between 3 September and 4 November, the pilots of the Cactus Air Force claimed to had shot down 268 Japanese aircraft in air combat, and to have damaged at least the same number of other aircraft.

Given the limited numbers of aircraft and quantities of fuel it possessed during the early stages of the Guadalcanal, the Cactus Air Force could not maintain a standing combat air patrol over Henderson Field. This placed a premium on the receipt of the earliest possible warning of the approach of Japanese aircraft so that US aircraft were not caught on the ground by Japanese air attacks. Here the work of the Australian coastwatcher organisation was invaluable in generating radio reports of aircraft passing over Bougainville, New Georgia and Santa Isabel islands in the direction of Guadalcanal, and the process was made more effective on 16 August when Lieutenant Commander Hugh Mackenzie of the Royal Australian Navy established a radio station at Henderson Field to monitor coastwatcher transmissions and relay their warnings to the Cactus Air Force.

There were also coastwatchers at several places around Guadalcanal, and with the aid of islanders these helped to rescue and return several Allied pilots during the campaign.

The Cactus Air Force’s dive-bombers and torpedo bombers sank or otherwise destroyed 17 major Japanese vessels, including the battleship Hiei, the heavy cruiser Kinugasa, the light cruiser Yura, the destroyers Asagiri, Murakumo and Natsugumo, and 12 transports, possibly sank one heavy cruiser and three destroyers, and severely damaged 18 other ships, including one heavy cruiser and five light cruisers. Most notable of these was Hiei, whose final destruction was achieved by Cactus Air Force warplanes, together with aircraft from the fleet carrier Enterprise and Boeing B-17 Flying Fortress four-engined heavy bombers from Espíritu Santo, after she had suffered serious damage from US cruisers and destroyers during the '1^st Naval Battle of Guadalcanal' on 13 November.

The 15 combat squadrons of the US Marine Corps which fought on Guadalcanal during this time lost 94 pilots killed or missing in action, with another 177 evacuated with wounds or sickness (especially severe malaria). Total figures for Japanese aircraft and aircrew losses during the Guadalcanal campaign have never been calculated.

The Guadalcanal campaign was of seminal importance in the development of US Marine Corps aviation in World War II. The most important lessons of the campaign were the demoralising effect on the ground forces of fighting without an umbrella of air superiority, the importance of using radar effectively, the vulnerability of Japanese transport and warship targets to air attack, and the overriding importance of the quick seizure and/or development of expeditionary airfields during amphibious operations.

The Cactus Air Force was replaced in April 1943, two months after the end of the Guadalcanal campaign, by the AirSols formation, which was a joint command for the Allied air units in the subsequent stages of the Solomon islands campaign up to June 1944. AirSols came under the command of Allied Pacific Ocean Areas in the form of Vice Admiral Aubrey W. Fitch, Commander, Aircraft, South Pacific, and absorbed the Cactus Air Force. AirSols controlled units of the US Navy, US Marine Corps, Royal New Zealand Air Force and the USAAF’s 13^th Army Air Force. Its opponents were the 11^th Air Fleet and Lieutenant General Kumaichi Teramoto’s 4^th Air Army, each based at Rabaul.

AirSols controlled the operations of all land-based aircraft in the Solomon islands campaign during 'Cartwheel', the major Allied offensive of 1943/44, and its first commander was Rear Admiral Charles P. Mason, who assumed the mantle of Mulcahy, who now became Mason’s chief-of-staff as well as commanding the 2^nd Marine Aircraft Wing.

On 15 June 1944, AirSols was replaced by AirNorSols (Air North Solomons), which eventually comprised 40 squadrons, including 23 of the US Marine Corps. On the same day, responsibility for Allied formations ands units to the west of 159° E and south of the equator passed from Nimitz’s Pacific Ocean Areas to General Douglas MacArthur’s South-West Pacific Area. However, seven USAAF squadrons in AirNorSols were later transferred, as part of Major General St Clair Streett’s 13^th AAF, to General George C. Kenney’s US Far East Air Forces, which came into existence on 3 August 1944 and also controlled the 5^th and 7^th AAFs, and eight US Navy and Royal New Zealand Air Force squadrons were moved to garrison duty in South Pacific.