A £3.1 million upgrade of the spiritual home of the Submarine Service has moved a step nearer completion after the centrepiece of the transformation was moved into place.

X24 is the sole survivor of the X-craft which raided German and Japanese shipping in supposedly safe havens in World War II.

Now the diminutive boat, for so long exposed to the wind and weather at the Royal Navy Submarine Museum in Gosport, can begin to take shelter after being lifted by crane into her new home.

The veteran submarine will sit at the heart of the Fieldhouse Building, a futuristic-looking exhibition hall being built opposite HMS Alliance at the Gosport memorial to the men of the deep.

Beyond protection from the elements, the multi-million pound centre – partly funded by Lottery money – will allow the 27-ton craft to be displayed properly, and her role and that of her sisters fully explained.

These miniature submarines were designed to extend the range of the Silent Service – they took the war to the enemy in shallow waters where their bigger conventional sisters could not venture.

They were a larger, more potent version of the open cockpit ‘human chariots’ deployed by the Italians and Japanese, and later the British – though in the case of the Japanese these chariots were invariably involved in suicide missions (the maritime equivalent of the aerial kamikaze) and if the pilot did not succeed in blowing himself up in a successful mission, he voluntarily went down with his vessel.

Training and equipment proved dangerous for the Axis operators, with both German and Japanese midget submarines proving troublesome and (again in the case of the Japanese) often only suitable for a one-way trip.

But the British took a different view, and a number of precision engineering firms – often miles from the sea, and with no shipbuilding heritage – took on the challenge of the X-craft building programme, which began in 1940 under the sponsorship of World War I submariner Cdr ‘Rabbit’ Rendell.

14 of the 30-ton X-craft were built, along with 11 of the slightly bigger XE-craft, were built, with an operational crew of four men.

Training was carried out on the west coast of Scotland using depot ship HMS Bonaventure, with support staff using HMS Varbel ashore.

On operations, an X-craft would be towed to the area by a mother submarine, using a passage crew of three, and once in position the four-man operational crew would replace them.

The craft would then slip towards its target, and once there (the diver having cut through nets, if necessary) limpet mines could be placed or the large side charges – large bombs on time fuses, set and released from inside the hull – set under the target ship’s hull.

Although cramped and uncomfortable, these boats were fine examples of engineering, with most of the features to be found on normal-sized boats, including a periscope.

They were powered by reliable Gardner diesel engines – the same plant which powered wartime London buses.

X-craft were responsible for the crippling of the German battleship Tirpitz and the Japanese cruiser Takao, winning their crews four Victoria Crosses.

X24 was twice committed on operations in the Norwegian fjords. In April 1944 she was sent to destroy floating docks in Bergen.

The first raid failed to destroy the docks, but X24 succeeded in despatching a merchantman. Sent back to destroy the docks in September 1944, X24 was successful.

“This secures her future and means we can do justice to the X-craft and the men who performed such brave and amazing exploits,” said museum director Cdr Jeff Tall.

Lasers were used to ensure the submarine, split into two parts, fitted together perfectly on the floor of the new building.

“This is a real milestone. X24 is the purpose for which this £3m extension is being built and will be the centrepiece,” Cdr Tall added.

“It was a poignant and historic moment seeing her get under way again, albeit on the back of a lorry, especially when you think of all the amazing journey she has had in the past.”

The new exhibition hall, shaped like a submarine and named after the late Admiral of the Fleet and champion of the Silent Service Sir John Fieldhouse, is due to open in July next year.