The big gun submarine cruiser

Early German development of submarine cruisers encouraged other nations to experiment before and during the Second World War.  

When the submarine was first conceived as a warship, its weapon was the torpedo. This would become a standard fit, and has remained so until today.  

However, it soon became clear with the outbreak of the First World War that a torpedo was an expensive way to sink a small vessel, and that a gun would be more economic. Hence, it became the norm to install a gun of up to 4in on deck to be used when the submarine was on the surface.  

Eventually larger guns were fitted, in addition to the usual outfit of torpedo tubes, to enable commerce war to be undertaken in a similar way to surface raiders. The result was the so-called submarine cruiser or U-cruiser.

Germany goes for larger guns

Britain’s sole submarine cruiser was HMS X1, which suffered numerous engine problems (Credit: worldnavalships.com)

By the second year of the First World War the Royal Navy’s blockade of Germany was causing massive shortages plan was hatched to build two cargo submarines for voyages to the US. The two were classed as merchant ships, able to carry 700 tons of cargo. Deutschland and Bremen were completed in 1916 and the former made two voyages, while the latter was lost on its maiden voyage. The success of the project led to six more being ordered. 

By 1917, the situation had changed, with the US siding with the allies. Deutschland was taken over by the Navy as U155, armed with two 15cm (5.9in) guns, and intended to operate as a heavily armed U-cruiser for commerce raiding.  

The six others were subsequently converted, while another 37 larger units were ordered as U139 to U150 and U173 to U200 although only four were commissioned before the end of the war.  

A more ambitious design was the Project 47 armoured U-cruiser, to be armed with four 15cm guns in single turrets. A similar updated design, the type XI, was proposed in 1937 but was not proceeded with. 

Britain’s X1

The French version of a submarine cruiser was the Surcouf, which was lost in mysterious circumstances in 1942, possibly by colliding with a merchant ship (Credit: naviearmatori.net)

In the early 1920s, the Royal Navy, impressed with the German submarine cruisers, decided to construct a British example. The resulting HMS X1 was armed with four 5.2in guns in two turrets, one before and one abaft the conning tower, which itself incorporated a telescopic range finder. 

Completed in 1926, she had a troublesome career due to machinery problems. Power was provided by two of the new Admiralty 3,000 bhp diesels and she suffered from severe torsional vibrations at full speed. In 1933, because of all the problems, she was retired from the Navy and was eventually scrapped in 1937. 

The French Surcouf 

The French Navy was similarly impressed and also experimented with a big gun submarine cruiser, building the Surcouf in 1929. She was armed with twin 8in guns in a turret, and also carried a Besson MB.411 floatplane for scouting. Surcouf served during the Second World War but was lost in February 1942 in the Caribbean. 

Changing demands 

Other nations also experimented with submarine cruisers. In 1926 the Japanese built the four J1 class with two 5.5in guns, while the US built two Narwhal class units armed with two 6in guns in 1928. Neither subsequently followed this line of development. 

While the German submarine cruisers had been fairly successful during the First World War, the concept proved less so compared with smaller submarines during the Second World War. Not only were they more expensive to build, they were vulnerable to damage from defensively equipped merchant ships, were slow to dive if found by aircraft, offered a large sonar echo underwater, and were less able to carry out avoiding manoeuvres during depth charge attacks. As a result, all navies concentrated on building smaller, cheaper, and more manoeuvrable submarines. 

The submarine monitor 

The extreme development of a big gun submarine was the Royal Navy’s three M class. Each was equipped with a 12in gun and designed to operate as a submersible monitor, capable of bombarding a shore from underwater.

John Barnes is a journalist and author and former editor of Marine Engineers Review.