J, K and N class destroyer

From Wikipedia, the free encyclopedia

J, K and N class

General Characteristics
Displacement:	1,690 tons (standard), 2,330 tons (full)
Length:	356 ft o/a (108.66 m)
Beam:	35 ft 8 in (10.87 m)
Draught:	9 ft (2.74 m)
Propulsion:	3 x Admiralty 3-drum boilers, steam turbines, 2 shafts, 40,000 shp
Speed:	36 kt
Range:	484 tons oil, 5,500 nm at 15 kt
Complement:	183 (218 as leader)
Armament (as built):
4 x twin 4.7 in L/45 QF Mark XII, mounting CP Mk.XIX 1 x quad 2 pdr "pom-pom" mount Mk.VII 2 x quad Vickers 0.5 in MG AA 2 x pentad tubes for 21 in torpedoes Mk.IX
Armament (war modifications):
3 x twin 4.7 in L/45 QF Mk.XII, mounting CP Mk.XIX 1 x single 4 in gun QF Mk.V on mounting HA Mk.III 1 x quad 2 pdr "pom-pom" mount Mk.VII Up to 4 x single and/or twin 20 mm Oerlikon guns 1 x quad tubes for 21 in torpedoes Mk.IX

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, eight each of ships with names beginning with J-, K- and N-. The flag superior of the pennant numbers changed from "F" to "G" in 1940.

1 Design history
2 Modifications
3 Service
4 J class
5 K class
6 N class
- 6.1 Royal Australian Navy
- 6.2 Royal Navy
7 External links

[edit] Design history

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.

Another advance was made in construction techniques, by the adoption of longitudinal framing - that is, the strength members around which the hull was built were the longitudinals, rather than the transverse frames. The bow form was also modified from that of the preceding Tribal class design; the clipper bow replaced by a straight stem with increased sheer. This change was not a success and as a consequence these ships were very wet forwards. This shortcoming was rectified from the S class onwards by returning to the earlier form.

Despite the vulnerability of the boiler layout, the design was to prove compact, strong and very successful, forming the basis of all Royal Navy destroyer construction from the O class up to the Cr class of 1944.

The armament was based on that of the Tribals, but replaced one twin 4.7 in L/45 QF Mark XII gun on mounting CP Mk.XIX with an additional bank of torpedo tubes. These mountings were capable of 40 ° elevation and 340 ° of training. Curiously, 'X' mounting was shipped so that the blind 20 ° arc was across the stern, rather than the more logical forward position where fire was obscured by the bridge and masts anyway. This meant that they were unable to fire dead astern. With the tubes now pentad, a heavy load of 10 torpedoes Mk.IX were now carried. The A/A armament remained the same, comprised of a quadruple 2 pdr gun Mark.VIII on mounting Mk.VII and a pair of quadruble Vickers 0.5 in machine guns, and was later to prove to be woefully inadequate. Fire control arrangements also differed from the Tribals, and the dedicated high-angle (H/A) rangefinder director was not fitted, instead only a 9 foot rangefinder was carried behind the usual destroyer director control tower (DCT). In the event, the rangefinder was heavily modified to allow it to control the main armament for A/A fire, and was known as the "3 man modified rangefinder".

The N class were ordered in 1940 as repeats of the J design, after delays and cost over-runs associated with the larger and more complicated L and M class. The only design change was to mount the 'X' 4.7 inch mounting in the more logical position with the 20° training blindspot forward. While building, the same early wartime modifications as the Js and Ks were applied, with a pair of twin power-operated 0.5 in machine gun turrets briefly carried on the quarterdeck before being replaced by single 20 mm Oerlikons.

[edit] Modifications

In 1940 and 1941, to improve the anti-aircraft capabilities, all ships had their after torpedo tubes landed and replaced with a single 4 inch gun QF Mark V on mounting HA Mark III. The useless multiple 0.5 inch machine guns were replaced with single 20 mm Oerlikon guns, with a further pair added abreast the searchlight platform amidships. The high-speed destroyer mine sweeps were replaced with a rack and two throwers for 45 depth charges and Radar Type 286 air warning was added at the masthead alongside Type 285 fire control on the H/A rangefinder-director.

In 1942 the 4 in gun was removed and the torpedoes returned to all surviving vessels. The 20 mm Oerlikon guns were replaced with twin mountings (except those on the quarterdeck) and Radar Type 291 replaced Type 286. Jervis, Kelvin, Nerissa and Norman had the searchlight replaced with the "lantern" for centimetric target indication Radar Type 271; Javelin and Kimberley having the lighter [[Type 272 fitted at the truck of the foremast. Napier, Nizam and Norseman (and later, Norman) had American Radar SG1 fitted at the head of a new lattice foremast, Norman replacing her Type 271 set with a single 40 mm Bofors gun. By the end of the war, the surviving J and K ships carried a lattice mast with Radar Type 293 target indication at the truck and Type 291 air warning at the head.

[edit] Service

Being amongst the Royal Navy's most modern and powerful destroyers at the outbreak of war, they were heavily committed. As a result, losses were heavy and of 24 ships built, six J, six K and one N class were war losses.