NAVYPEDIA

Photo

J4 1919

Ships

Name	No	Yard No	Builder	Laid down	Launched	Comp	Fate
J1 (3/1919- RAN)			Portsmouth DYd	4.1915	6.11.1915	4.1916	sold 2.1924
J2 (3/1919- RAN)			Portsmouth DYd	5.1915	6.11.1915	7.1916	sold 2.1924
J3			Portsmouth DYd	1915	---	---	cancelled 4.1915
J4			Portsmouth DYd	1915	---	---	cancelled 4.1915
J3 (ex-J7) (3/1919- RAN)			Pembroke DYd	3.1915	4.12.1915	6.1916	sold 1.1926
J4 (ex-J8) (3/1919- RAN)			Pembroke DYd	3.1915	2.2.1916	8.1916	sold 2.1924
J5 (3/1919- RAN)			Devonport DYd	4.1915	9.9.1915	5.1916	sold 2.1924
J6			Devonport DYd	4.1915	9.9.1915	7.1916	sunk 15.10.1918
J7 (3/1919- RAN)			Devonport DYd	8.1916	21.2.1917	11.1917	sold 11.1929

Technical data

Displacement standard, t
Displacement normal, t	J1 - 6: 1204 / 1820 J7: 1212 / 1820
Length, m	J1 - 6: 84.0 J7: 83.7
Breadth, m	7.02
Draught, m	4.27
No of shafts	3
Machinery	3 12-cyl Vickers diesels / 3 electric motors
Power, h. p.	3600 / 1350
Max speed, kts	19.5 / 9.5
Fuel, t	diesel oil 91
Endurance, nm(kts)	5000(12.5)
Armament	J1 - 5: 1 x 1 - 76/30 10cwt QF Mk II, 1 x 1 - 76/28 12pdr 8cwt QF Mk I, 6 - 450 TT (4 bow, 2 beam, 12) J6: 1 x 1 - 76/30 10cwt QF Mk II, 1 x 1 - 40/37 2pdr QF Mk III, 6 - 450 TT (4 bow, 2 beam, 12) J7: 1 x 1 - 76/45 20cwt QF Mk II, 1 x 1 - 40/37 2pdr QF Mk III, 6 - 450 TT (4 bow, 2 beam, 12)
Complement	44
Diving depth operational, m	50

Standard scale images

Graphics

Project history

The continuing incorrect intelligence reports of 22kt U-boats so worried the C-in-C of the Grand Fleet that he lobbied successfully for yet another attempt at a fleet submarine, capable of keeping station with the battle fleet. Vickers, already wrestling with the engines for the Nautilus, did not propose to use the 1850hp diesel, and suggested instead that the standard 8-cyl engine could be enlarged to 12-cyl, but it would still take three, and although 20kts was the speed asked for, the records suggest that 19.5kts was the accepted design-speed. Given the haste with which the design was to be prepared the Admiralty had no choice, and approved its one and only triple-shaft design in January 1915. The design was another partial double-hull type, with the double hull occupying 56% of the length. As built the large free-flooding casing brought the bows down in a seaway, slowing the boat down, so it was sealed off. After some months in service all had their bows raised, and thereafter could make 17kts in the heaviest seas.

Originally eight boats were approved, all from the Royal Dockyards, but two from Portsmouth DYd, J3 and J4, were cancelled and J7 and J8 were renumbered to fill the gap. A further boat was ordered for the RAN but she differed in important respects. The control room was moved from just forward of the beam TT to the motor room aft. The conning tower was therefore moved aft as well, but in other respects J7 was identical to her sisters.

Modernizations

about 1917, J1: + DC racks

1917-1918, J1: - 1 x 1 - 76/30, 1 x 1 - 76/28; + 1 x 1 - 102/40 BL Mk XI, 1 x 1 - 40/37 2pdr QF Mk III

1917-1918, J2, J4: - 1 x 1 - 76/30, 1 x 1 - 76/28; + 1 x 1 - 102/40 QF Mk IV, 1 x 1 - 40/37 QF Mk III

1917-1918, J5: - 1 x 1 - 76/30, 1 x 1 - 76/28; + 1 x 1 - 102/41 QF Mk VII, 1 x 1 - 40/37 QF Mk III

1917-1918, J6: - 1 x 1 - 76/30; + 1 x 1 - 102/41 QF Mk VII

1917-1918, J7: - 1 x 1 - 76/45; + 1 x 1 - 102/41 QF Mk VII

Naval service

J6 was sunk in error by British decoy ship Cymric 15.10.1918 off Blyth.