I have a copy of a British Intelligence report dated 12 February 1925
that says that four naval ratings at Chatham (a naval dockyard) were
Soviet spies who were reporting on the performance of Submarine X.1.

What was special about Submarine X.1.?

Dear Bryan, 

The X-1 Class Submarine was to be launched on November 1923, and was
supposed to be special in three aspects aspects.

The submarine was, first of all, larger than any other submarine
previously built ("Besides six 21in. bow torpedo tubes she carried two
twin 5.2in. gun turrets. In theory she could make 19.5 knots on the
surface, and at economical speed she had a greater range than normal
cruisers; but her diesels continually broke down and she was plainly
vulnerable to counter-fire from ships and bombing by aircraft."
SOURCE: Winding Down and Working Up, Navy News)

Not only that, but the submarine was supposedly "a large submarine for
commerce raider, an idea which held a fascination for world powers at
that time." (SOURCE: X 1 Class,
<http://members.iinet.net.au/~eadej/x1class.html>).

It also had its own unique gun: "This weapon was specifically
developed for the submarine X 1, which was the British version of the
"submarine cruiser."  These were submarines with large-caliber
armament built by many nations in the 1920s, none of which were really
successful.  For the X 1, the design concept was that she should be
able sink or disable a destroyer at 6,000 yards (5,500 m) with her
guns alone.  In practice, this was unlikely, as the low height above
the water of the range finding equipment and the unsteady nature of a
submarine made this craft unsuitable as a gun platform." (SOURCE:
5.2"/42 (13.2 cm) QF Mark I,
<http://www.warships1.com/Weapons/WNBR_52-42_mk1.htm>).

Less important to the Soviets, the X-1 was the first submarine to
originate from the Chatham Dockyards.

See also : 
ADM 116-2219: Cruise of the Special Service Squadron 1923- 24
<http://www.hmshood.org.uk/reference/official/adm116/adm116-2219.html>,
p. 13 (a letter concerning a cruise to the dominions, and to the
objection to launch the X1 in this cruise).

COMPTON-HALL R.: SUBMARINE WARFARE - MONSTERS AND MIDGETS Blandford. 1985

I hope this answered your question. I searched the web for the
submarine's name, and (since X-1 was also a name of an American
experimental submarine) also with terms such as the dates or the
places mentioned.

Please contact me if you need any clarification on this answer before you rate it.

---

Clarification of Answer by politicalguru-ga on 18 Feb 2004 14:36 PST

Sorry, the Navy News URL appeared to have sank underwater. Here it is:
<http://www.navynews.co.uk/articles/2001/0112/1001121201.asp>

Brilliant, PG, Many thanks!

With piccies, too.

I am seriously impressed.

How would I manage without you?

Warmest regards

Bryan