HMS X1 HM Submarine " X1 " was conceived and designed as a submersible commerce raider for the Royal Navy ; at the time of her launching she was the largest submarine in the world . The idea of a submarine cruiser had been proposed as early as 1915 , but was not put into practice until 1921 . " X1 " , which was based on the uncompleted German " U - 173 " class of 2 , 000 - ton " U - Cruisers " , was laid down on 2 November 1921 at the Naval Dockyard Chatham and completed on 23 September 1925 , commissioning in December 1925 . The 1922 Washington Naval Treaty , of which Britain was a signatory , did not ban submarines but it did ban their use against merchant ships , which was " X1 " s unacknowledged purpose ; its armament had been designed to successfully engage the classes of vessels likely to be escorting convoys , such as destroyers and frigates . Therefore , a certain amount of secrecy surrounded " X1 " , the government even going to the lengths of taking a national newspaper to court over its pictures of the new submarine following her launch , all copies of the paper being seized . Description . The " X1 " s thick pressure hull was in diameter amidships , and was divided into 10 water - tight compartments . This was almost completely surrounded by her external hull which also contained the main ballast tank s and most of her fuel . Her intended maximum diving depth was but was reduced to once in service . She was expected to sink her targets using gunfire and so was given four guns to be able to defeat a destroyer or armed merchant ship although she was fitted with six bow tubes for torpedoes to supplement her guns . Armament . " X1 " carried four QF 5 . 2 inch Mk I guns in twin unarmoured turrets , one forward and one aft of the conning tower . They had a range of about . A circular trunk ran from each mounting to the magazine in the pressure hull which contained 100 rounds per gun . A working chamber which was in diameter encircled the trunk between the pressure hull and the gun mount . Her ammunition hoists were problematic and could not sustain the desired rate of fire of six rounds per gun per minute . Special ballast tanks were used to compensate for the loss of weight as ammunition was fired . Working and control of the guns required no less than 58 crewmen . The fire - control tower was in the middle of the sail and had a top that could be raised when in use . The upper control room was between the tower and the pressure hull . Just aft of the control room was the rangefinding room with a rangefinder on the bridge that could be raised . Her six torpedo tubes came from a cancelled L - class submarine and she was provided with one reload for each tube . It took some 24 minutes to reload them all because her torpedo room was space restricted . Propulsion . The main engines were two 8 - cylinder Admiralty diesel engines with a total output of . Two auxiliary MAN Diesel engines taken from " U - 126 " were installed for battery charging purposes . For underwater propulsion , two GEC electric motors of each were fitted . It was hoped to achieve over using both Diesels and electric motors together , but the highest power achieved ( during a full power trial in March 1926 ) was . She had three groups of batteries , each with 110 cells weighing a total of . In theory she could make on the surface , and at economical speed she had a greater range than normal cruisers , but both sets of diesel engines suffered from continual mechanical problems that reduced her speed and range . The " X1 " s average diving time ( to periscope depth ) was 2 minutes 20 seconds . Her handling underwater was considered superior to other submarines of the period . Career . After " X1 " was commissioned in December 1925 and accepted in April 1926 she made a voyage to Gibraltar after which her main engine drive wheels were found to be damaged . After repairs she was sent to the Mediterranean Sea . Her starboard shaft broke during a full - power run in January 1928 and a new set of gears was needed , but after refitting at Malta her port shaft broke in the same place in April 1928 . By 1930 her commanding officer reported " internal arrangements not very satisfactory because of overcrowding with auxiliary machinery , accommodation is cramped , ventilation poor and the ship suffers from humidity , diving arrangements good . " Both the main and auxiliary engines were troublesome and she spent most of her time under repair , before being laid up . " X1 " was placed in reserve after 1930 , before she was finally scrapped at Pembroke on 12 December 1936 .