- Class: Arethusa - 4 cruisers of 1932-35
- Displacement: 5,270 tons
- Dimensions: 480 (pp) 506 (oa) x 51 x 14 ft
- Machinery: 4-shaft geared turbines, SHP 64,000 = 32.25 knots
- Armor: Main belt 2in, deck 2in, turrets 1in, DCT 1in
- Armament: 6-6in (3x2), 8-4in AA (4x2), 8-.5in AA (2x4) guns, 6-21in (2x3) TT; 1 aircraft
- Complement: 500
- Builder: Harland & Wolff (Belfast)
- Laid Down: 30 May 1934
- Launched: 15 Oct 1935
- Completed: 12 Nov 1936
- Service: 3rd CS Mediterranean Fleet, Sep-Dec 1939. 2nd CS Home Fleet, Jan-Jul 1940. During Norwegian campaign, she was damaged by grounding 9 Apr off Vestfjord, damaged by bombs 10 Apr, and again by grounding 11 Apr. Repairs and refitting May 1940-June 1941. 2nd CS Home Fleet, Apr-Nov 1941. 15th CS Mediterranean Fleet Dec 1941-May 1942. Joined Force 'K' based on Malta and on 9 Nov 1941 with sister Aurora and destroyers Lance and Lively, intercepted an Italian convoy heading for Tripoli and sank seven merchant ships (40,000 GRT total) and destroyer Fulmine and damaged two others (one of which was sunk by submarine Upholder the next day.
Slightly damaged by mine off Tripoli 19 Dec 1941; companion Neptune had run into minefield and exploded two, then a third and fourth and was lost.
At the Second Battle of Sirte 22 Mar 1942, Penelope sailed from Malta to join an escort of light cruisers and destroyers covering a supply convoy coming from Alexandria. This weak force succeeded in driving off a strong Italian squadron including battleship Littorio and several 8" cruisers. The battle was the inspiration for C.S.Forester's novel "The Ship."
Damaged by bombing at Malta 26 Mar 1942, and again on 4 Apr and 8 Apr. Repairs and refit in USA, Jun-Sep 1942. Portsmouth working up Oct-Dec 1942. 12th CS Western Mediterranean Jan-Jul 1943; damaged by shell fire 1 Jun 1943. Force 'Q' and Force 'K' Oct-Dec 1943; damaged by unexploded bomb in Aegean 7 Oct 1943. 15th CS Mediterranean Fleet Dec1943-Feb 1944.
Torpedoed and sunk by German submarine U410 off Anzio 18 Feb 1944