'Ironclad' was the British seizure of Diégo Suarez and Antsirane on the northern coast of the Vichy French island of Madagascar, so paving the way for subsequent 'Stream Line' operations for the capture of the entire island (5 May/6 November 1942).

The strategic desirability of Madagascar in World War II was the area of Antsiranana, which is a large bay with a fine harbour on the northern tip of the island, and this possesses an opening to the east through a narrow channel called the Oronjia Pass. The Vichy French naval base of Antsirane lay on a peninsula between two of the four smaller bays within Antsiranana Bay. This larger bay bites deeply into the northern peninsula of Madagascar, whose most northerly point is Cap Amber, almost severing it from the rest of the island. In the 1880s Antsiranana Bay came to be coveted by France, which claimed it as a coaling station for steamships travelling to French possessions in the east, and the French seizure of the island was formalised after the 1^st Franco-Hova War (1883/85), after which Queen Ranavalona III signed a treaty on 17 December 1885 giving France a protectorate over the bay and surrounding territory, as well as the islands of Nosy Bé and Ste Marie de Madagascar. The colony’s administration was subsumed into that of French Madagascar in 1897 following the end of the 2^nd Franco-Hova War (1894/95).

In 1941, the town of Antsirane, the bay and the channel were well protected by naval shore batteries.

After their conquest of South-East Asia, largely by the end of February 1942, the Japanese high command was able to consider the possibility of moves westward into the Indian Ocean. With ranges in the order of 10,000 miles (16000 km), making them the longest-ranged boats in the world at the time, the fleet submarines of the Imperial Japanese navy were moving freely throughout the northern and eastern expanses of the vast Indian Ocean, and in March 1942, Japanese aircraft carriers undertook the 'C' raid deep into the Indian Ocean. This raid drove Vice Admiral Sir James Somerville’s technically as well as numerically outclassed British Eastern Fleet out of the area from its main base at Trincomalee in Ceylon to Kilindini, the harbour of the Kenyan city of Mombasa and they were forced to relocate to a new base at Kilindini (the port of Mombasa in Kenya) on the coast of East Africa.

The British believed that Japan’s developments after this time might include greater territorial ambitions, but would more probably take the form of the sea and air interdiction of the UK’s maritime lines of communications with the Middle East, India, Australia and New Zealand, which were vulnerable to attack by aircraft, surface ships and submarines in their routes across the Arabian Sea toward the Red Sea and the Suez Canal, and across the Indian Ocean and along the East African coast toward South Africa.

The retirement to Kilindini made British warships and merchant vessels more vulnerable to attack as the Japanese might be able to use Madagascar’s naval basing facilities, and thus the possibility of Japanese naval forces making use of forward bases in Madagascar had to be addressed. The potential use of these facilities particularly threatened Allied merchant shipping, the supply route to the British forces in the Middle East and North Africa, India and Australasia.

Given their range, Japanese fleet submarines operating from bases on Madagascar would pose an immense threat to the Allied lines of communications across a region stretching from the Pacific and Australia, to the Middle East and as far as the South Atlantic.

On 17 December 1941, Vizeadmiral Kurt Fricke, the chief-of-staff of the German Seekriegsleitung (maritime warfare command), met Vice Admiral Naokuni Nomura, the Japanese naval attaché in Germany, to discuss the delimitation of operational areas for the German and Japanese navies. At another meeting on 27 March 1942, Fricke stressed the importance of the Indian Ocean to the Axis powers and expressed the desire that the Japanese begin operations against the Allied lines of maritime communication through the northern part of the Indian Ocean. Fricke also emphasised that Ceylon, the Seychelles island group and Madagascar should have a higher priority for the Axis navies than operations against Australia. By 8 April, the Japanese had informed Fricke that they intended to commit four or five submarines and two auxiliary cruisers to operations in the western part of the Indian Ocean between Aden in the north and the Cape of Good Hope in the south, but refused to disclose their plans for operations against Madagascar and Ceylon, only reiterating their general commitment to operations in the area.

Decrypts of intercepted Japanese signals had given the Allies an insight into Japanese plans for the Indian Ocean and on 27 November 1941, the British Chiefs-of-Staff discussed the possibility that the Vichy French government might cede the whole of Madagascar to Japan, or alternatively permit the Japanese navy to establish bases on the island. British naval advisers urged the occupation of the island as a precautionary measure. On 16 December, Général de Brigade Charles de Gaulle, leader of the Free French movement in London, sent a letter to Prime Minister Winston Churchill pressing the desirability of a Free French operation against Madagascar. Churchill was all too aware of the risk posed by a Japanese-controlled Madagascar to naval and mercantile shipping in the Indian Ocean, and especially that plying the strategically vital route to India and Ceylon, and considered the facilities in Antsiranana Bay, most particularly the ports of Antsirane and Diégo Suarez (opposite Antsirane on the eastern shore of the Andrakaka peninsula in Antsiranana Bay) as the strategic key to Japanese influence in the Indian Ocean. However, Churchill also made it clear to planners that he did not feel that the UK currently possessed the resources to mount such an operation and, following experience in the abortive 'M' (i) operation to take Dakar in French West Africa during September 1940, did not wish to entertain a joint operation by British and Free French forces to secure the island.

By 12 March, though, Churchill had been convinced of the importance of such an operation, and it was thereupon decided that the planning for the invasion of Madagascar would begin in earnest. It was agreed that the Free French would be explicitly excluded from the operation. As a preliminary outline, Churchill gave the following guidelines to the planners for what was at the time designated as 'Bonus': Force 'H', the naval force guarding the western part of the Mediterranean, should move to the south from Gibraltar after being replaced at Gibraltar by elements of the Home Fleet; the 4,000 men and the ships proposed for the undertaking by Commodore the Lord Mountbatten, the Chief of Combined Operations, should be retained as the nucleus around which the plan should be built; the operation should start on about 30 April 1942; and in the event of success, the commandos recommended by Mountbatten should be replaced by garrison troops as soon as possible.

The depleted Home Fleet was to be bolstered, in the short term, by the US loan of Task Force 39 commanded by Rear Admiral John W. Wilcox. This departed Casco Bay, Maine, on 25 March bound for Scapa Flow in the Orkney islands group with the battleship Washington, fleet carrier Wasp, heavy cruisers Tuscaloosa and Wichita, and destroyers Ellyson, Livermore, Long, Madison, Plunkett, Sterett, Wainwright and Wilson.

The Allied leadership accordingly decided to launch the 'Ironclad' (originally 'Bonus' and then 'Extend') amphibious assault on Madagascar with the northern port and naval base of Diégo Suarez and Antsirane as the primary objective. The expedition was mounted by forces from the UK under the escort of parts of Vice Admiral E. N. Syfret’s Gibraltar-based Force 'H', the rendezvous being made in South Africa where the whole force came under Syfret’s command, with Major General R. G. Sturges commanding the land forces, known as Force 121 and established on 14 March.

The convoy which left the Clyde river in the UK on 23 March carrying elements of Major General H. M. P. Berney-Ficklin’s 5^th Division comprised the 20,119-ton Duchess of Atholl, 20,175-ton Franconia, 5,853-ton Greystoke Castle carrying 163 vehicles and fuel, 9,891-ton infantry landing ship Karanja, 9,890-ton infantry landing ship Keren, 11,030-ton Free Polish Sobieski and 20,012-ton Winchester Castle. The naval portion of 'Ironclad' comprised the elderly battleships Ramillies and Warspite, the fleet carriers Illustrious (four squadrons with 40 aircraft) and Indomitable (five squadrons with 42 aircraft), the heavy cruiser Devonshire, the light anti-aircraft cruiser Hermione, the destroyers Active, Anthony, Duncan, Inconstant, Javelin, Laforey, Lightning, Lookout, Pakenham, Paladin, Panther and Australian Nizam and Norman, the corvettes Auricula, Freesia, Cyclamen, Fritillary, Genista, Jasmine, Nigella and Thyme, and the minesweepers Cromarty, Cromer, Poole and Romney.

The all-British Force 121 comprised Brigadier V. C. Russell’s 13^th Brigade (three battalions) and Brigadier G. W. B. Tarleton’s 17^th Brigade (three battalions) of the 5^th Division, which had been earmarked for service in the Western Desert but which was now split up into brigades for detached service, Brigadier F. W. Festing’s 29^th Independent Brigade Group (four battalions, one battery of light artillery, one machine gun company and one Special Service Squadron with six Valentine infantry tanks and six Tetrarch light tanks), and Lieutenant Colonel W. S. S. Sanguinetti’s No. 5 (Royal Marine) Commando. Units which arrived later in the campaign were Brigadier W. A. Dimoline’s 22^nd (East Africa) Brigade Group to replace the 13^th and 17^th Brigades, Brigadier R. E. Hobday’s 27^th (North Rhodesia) Brigade (three battalions, one battery of field artillery and one battalion of light artillery) and Brigadier G. T. Senescall’s South African 7^th Motorised Brigade.

The Vichy French forces, under the overall command of the island’s governor, Armand Léon Annet, included about 8,000 troops, of whom about 6,000 were Madagascan (most of them in the two Régiments Mixte Malgache) and most of the other 2,000 Senegalese. Between 1,500 and 3,000 of these Vichy French troops were concentrated around Diégo Suarez. On the island’s west coast were two platoons of reservists and volunteers at Nossi-Bé, two companies of a Régiment Mixte Malgache at Ambanja and one battalion of a Régiment Mixte Malgache at Majunga; on the east coast were one battalion of a Régiment Mixte Malgache at Tamatave; one section of 65-mm (2.56-in) guns at Tamatave and one company of a Régiment Mixte Malgache at Brickaville; in the centre of the island were three battalions of a Régiment Mixte Malgache at Tananarive, one motorised reconnaissance detachment at Tananarive, one battery of artillery at Tananarive, one section of 65-mm (2.56-in) guns at Tananarive, one engineer company at Tananarive, one company of a Régiment Mixte Malgache at Mevatanana and one company of the Bataillon de Tirailleurs Malgaches at Fianarantsoa; and in the south of the island were one company of the Bataillon de Tirailleurs Malgaches at Fort Dauphin and one company of the Bataillon de Tirailleurs Malgaches at Tuléar.

The Vichy French naval and air defences were relatively light and/or obsolete: eight coastal batteries, two armed merchant cruisers, two sloops, five submarines including Bévèziers, Héros and Monge, 17 Morane-Saulnier MS.406 fighters of the 565^th Escadrille at Ivato-Tananarive and 10 Potez 63.11 bombers of the 555^th Escadrille also at Ivato-Tananarive.

During the assembly of the 'Ironclad' force in Durban, Field Marshal Jan Smuts pointed out that the mere seizure of Diégo Suarez would not provide any guarantee against continuing Japanese aggression, and this urged that the ports of Majunga and Tamatave also be occupied. This suggestion was evaluated by the Chiefs-of-Staff, who decided for lack of manpower to retain Diégo Suarez as the only objective. Churchill remarked that the only way in which the British to secure Madagascar on a permanent basis was by means of a strong fleet and adequate air support operating from Ceylon, and sent General Sir Archibald Wavell, commanding in India, a note stating that as soon as the initial objectives had been met, all responsibility for the defence of Madagascar would be devolved onto India Command. Churchill added that when the No. 5 Commando was withdrawn, garrison duties would be performed by two East African brigades and one brigade from the Belgian Congo or West Africa.

In March and April, aircraft of the South African Air Force undertook reconnaissance flights over the Diégo Suarez area, and Nos 32, 36 and 37 Coastal Flights were withdrawn from maritime patrol operations and sent to Lindi on the Indian Ocean coast of Tanganyika, with an additional 11 Bristol Beaufort torpedo bombers and six Martin Maryland light bombers to provide close air support during the planned operation.

The 'Y' (i) slow convoy departed Durban on 25 April with two special landing ships (gantry landing ship Derwentdale and tank landing ship Bachaquero), six supply and motor transport ships (City of Hong Kong, Empire Kingsley, Mahout, Mairnbank, Martand II and Thalatta) and one hospital ship escorted by the cruiser Devonshire, three destroyers, the 3^rd Escort Group, and the 14^th Minesweeping Flotilla (Cromarty, Cromer, Poole and Romney).

The 'Z' (ii) fast convoy, carrying Force 151, followed three days later with five attack transports (Karanja, Keren, Royal Ulsterman, Sobieski and Winchester Castle) and three troop transports (Duchess of Atholl, Franconia and Oronsay) escorted by part of Syfret’s force (battleship Ramillies, carrier Illustrious, light anti-aircraft cruiser Hermione and six destroyers).

On 3 May, the convoys and the reinforcement detached from Somerville’s Eastern Fleet, under the command of Rear Admiral D. W. Boyd and comprising the fleet carrier Indomitable and two destroyers, joined the British invasion force. From there, Captain G. N. Oliver’s invasion fleet reached an area to the north-west of the island with the cruiser Devonshire, destroyers Anthony, Laforey, Lightning and Pakenham corvettes Auricula, Cyclamen, Freesia, Fritillary, Genista, Jasmine, Nigella and Thyme, the four minesweepers, and the transports.

The covering force operated farther offshore with the battleship Ramillies, carriers Illustrious and Indomitable, and destroyers Active, Duncan, Inconstant, Javelin, Lookout, Paladin and Panther. The cruiser Hermione meanwhile undertook a diversionary sortie.

On 5 May carrierborne aircraft attacked the French airfields and ships. The Vichy French auxiliary cruiser Bougainville was sunk by aircraft from Illustrious and the submarine Bévèziers was depth-charged and sunk: the boat was later raised.

On the basis of the reconnaissance sorties flown by South African Air Force aircraft from East Africa, the British landed from 04.30 on 5 May. As noted above, the primary object of was the naval base of Diégo Suarez, located at Antsirane in Antsiranana Bay to the east of Diégo Suarez proper, but as access to this bay was controlled by French batteries it had been thought tactically wise to land in Courrier Bay, where Auricula was mined and damaged at 11.40 on 6 May, to the west of the isthmus connecting Cap Amber with the mainland. The assault forces were ferried ashore by landing craft and met no resistance, and No. 5 Commando then launched an overland advance of some 12 miles (19 km) to take Diégo Suarez, while the main force advanced to the south-east in order to cut off Antsirane. While the landing and the first stage of the advance progressed without undue difficulty, the attack on Antsirane was then checked by strong Vichy French defences in the rear of Antsirane, defences that had not been revealed by the photo-reconnaissance flights. The landing of Royal Marines commandos by the destroyer Anthony near Antsirane at 20.50 on 6 May and the subsequent capture of important central installations led, however, to the rapid collapse of French resistance.

The colonial sloop d’Entrecasteaux, which had provided gunfire support for the defence, had to be run aground after being hit by bombs from aircraft from Indomitable and the gunfire of the destroyer Laforey. On 7 May the Vichy French submarine Héros was sunk by the corvette Genista and aircraft from Illustrious while trying to attack the British main force. On 8 May the submarine Monge unsuccessfully attacked Indomitable before being sunk by the destroyers Active and Panther. The Vichy French submarine Glorieux and colonial sloop d’Iberville escaped to southern Madagascar and thence, later, to Toulon.

The loss of Antsirane demoralised the Vichy French defence, whose men then started to surrender rapidly, and 'Ironclad' proper had been completed by the early morning of 7 May.

A diversionary attack had also been staged in the east. Air cover was provided mainly by Fairey Albacore, Fairey Swordfish and Grumman Wildcat aircraft of the Fleet Air Arm, which attacked Vichy French shipping. A small number of South African aircraft aided this largely British effort. Significant Vichy French forces withdrew from the area of Diégo Suarez toward the south, and now put up a stronger defence than had been anticipated.

Reinforcements were received by each side. In the case of the Vichy French, the Japanese submarines I-10, I-16 and I-20 arrived on 29 May to be joined later by I-18, and a reconnaissance aeroplane from I-10 spotted Ramillies at anchor in Diégo Suarez harbour. However, the aeroplane was seen and Ramillies changed berth. I-16 and I-20 each launched a midget submarine (M-16b and M-20b), one of which managed to enter the harbour and fire two torpedoes while under depth charge attack from two corvettes. One torpedo severely damaged Ramillies, while the second sank an oil tanker. The two men of the crew beached their submarine and fled inland, where both were killed by Royal Marines three days later.

Hostilities then continued at a low level for several months in 'Stream Line'. The 5^th Division was transferred to India from 19 May, and Dimoline’s 22^nd (East Africa) Brigade Group arrived on 8 June, Senescall’s South African 7^th Motorised Brigade on 24 June and Hobday’s 27^th (North Rhodesia) Brigade Group (including forces from East Africa) on 8 August. The British 29^th Independent Brigade Group and the 22^nd (East Africa) Brigade Group carried out the 'Stream' and 'Tamper' amphibious landings on 10 September at Majunga and Morondava, in the north-west of the island, to revitalise Allied offensive operations before the opening of the rainy season, and in September other landings were effected at strategic points round the island ('Jane' at Tamatave on 18 September, and Fort Dauphin and 'Rose' at Tuléar on 29 September). Progress was slow, for in addition to occasional small-scale clashes with Vichy French forces, the Allied units also encountered scores of obstacles erected on the main roads by Vichy French soldiers. The Allies eventually captured the capital, Tananarive, on 23 September without much opposition, and also the town of Ambalavao on the road south through the centre of the island toward Ihosy, where it separated to reach the ports of Tuléar in the south-west and Fort Dauphin in the south-east.

The last major action was at Andriamanalina on 18 October, and Annet surrendered near Ihosy, in the southern half of the island, on 5 November. The Allies had suffered about 500 casualties in the landing at Diégo Suarez, as well as 30 killed and 90 wounded in the operations which followed 10 September.