J-, K- and N-class destroyer

HMS Kashmir
Class overview
Operators:	Royal Navy  Royal Australian Navy  Polish Navy  Royal Netherlands Navy  Indonesian Navy
Preceded by:	Tribal class
Succeeded by:	L and M class
Subclasses:	J, K, N
Built:	1937–41
Planned:	25
Completed:	24
Cancelled:	1
Lost:	15
Scrapped:	9
General characteristics (J and K classes as built)
Type:	Destroyer
Displacement:	1,690 long tons (1,720 t) (standard) 2,330 long tons (2,370 t) (deep load)
Length:	356 ft 6 in (108.7 m) o/a
Beam:	35 ft 9 in (10.9 m)
Draught:	12 ft 6 in (3.8 m) (deep)
Installed power:	44,000 shp (33,000 kW) 2 × Admiralty 3-drum boilers
Propulsion:	2 × shafts; 2 × geared steam turbines
Speed:	36 knots (67 km/h; 41 mph)
Range:	5,500 nmi (10,200 km; 6,300 mi) at 15 knots (28 km/h; 17 mph)
Complement:	183 (218 for flotilla leaders)
Sensors and processing systems:	ASDIC
Armament:	3 × twin QF 4.7-inch (120 mm) Mk XII guns 1 × quadruple QF 2-pounder anti-aircraft guns 2 × quadruple QF 0.5-inch (12.7 mm) Mk III anti-aircraft machineguns 2 × quintuple 21-inch (533 mm) torpedo tubes 20 × depth charges, 1 × rack, 2 × throwers
General characteristics (N class where different)
Displacement:	1,773 long tons (1,801 t) (standard) 2,384 long tons (2,422 t) (deep load)
Armament:	1 × single QF 4-inch Mark V (102 mm) AA gun 4 × single 20 mm (0.8 in) Oerlikon AA guns 2 × twin QF 0.5-inch Mk III machineguns 1 × quintuple 21-inch torpedo tubes 45 × depth charges, 1 × rack, 2 × throwers

The J, K and N class was a class of 24 destroyers of the Royal Navy launched in 1938. They were a return to a smaller vessel, with a heavier torpedo armament, after the Tribal class that emphasised guns over torpedoes. The ships were built in three flotillas or groups, each consisting of eight ships with names beginning with "J", "K" and "N". The flag superior of the pennant numbers changed from "F" to "G" in 1940.

The ships were modified throughout their wartime service, particularly their anti-aircraft (AA) guns; they were also fitted with radar.

The design was intended as a smaller follow-on from the preceding Tribal class, and incorporated one radical new idea that was a departure from all previous Royal Navy destroyer designs. That was the adoption of a two boiler room layout. This reduced hull length and allowed for a single funnel, both reducing the profile and increasing the arcs of fire of the light anti-aircraft (A/A) weapons. However, this also increased vulnerability, as there were now two consecutive large compartments with the resultant risk of a single well placed hit flooding both and resulting in a total loss of boiler power. This illustrates somewhat the Admiralty's attitude to the expendable nature of destroyers. This is of course, as opposed to the 3-boiler-room layout that was used starting with the F class in the early 1930s. Early ships also tended to use twin boiler rooms, which are still a great improvement over a single boiler room. In any case, destroyers are lightly armored and fast vessels meant to survive by avoiding being hit at all. The odds of a single hit striking just the right spot to disable both boiler rooms simultaneously were considered remote enough to be worth risking in exchange for the benefits given by a two-room layout. During Prewar trials "...On a light displacement Jackal attained 37.492 knots, on the Arran mile in 60 fathoms, 34.37 knots deep. Jupiter in 75 fathoms made 33.835 knots light, 33.045 knots deep displacement."

A significant advance in construction techniques was developed by naval architect Albert Percy Cole. Instead of going for transverse frame sections which were unnecessarily strong, but held together by weak longitudinals, Cole went for extra strong longitudinals and weaker transverse frames.

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Wikipedia