"M" Class Destroyer (1914)

A total of 103 destroyers of the "M" Class were completed, 13 in the 1913-1914 programme and 90 further ships as part of the successive orders of the War Emergency Programme.

They were essentially improved "L" class destroyers with 6 knots more speed, but there was a mix of Admiralty design vessels (79) and a diverse set of builder's specials (22 ships).

The War Emergency Programme ships are often called the Repeat "M" Class, but the distinction between them and the original 13 vessels is largely fiduciary and less important than the design differences attributable to specials and Admiralty design as well as the manic diversity the Royal Navy's ships exhibited even when it intended a uniform class. For this convoluted reason, "Repeat 'M' Class" will be used in a passing manner here, and all 103 ships generally called "M" class destroyers.

Machinery

Generators

In 1916, it was stated that "new destroyers" have two 26.25 kw dynamos arranged in parallel. It is possible that this applied to some or all of this class.

Performance

Admiralty M

The ships' capacity for 285 tons of fuel, delivered the following endurance.

Knots	Tons / hour	Endurance (hours)	radius (nm)
14	2.0	135	1,890
16	2.5	108	1,728
18	3.2	84	1,512
20	4.0	67	1,340
22	5.0	54	1,1188
24	6.2	43	1,032
26	8.2	33	858
28	10.8	25	700
30	12.5	21	630

Yarrow M

The ships' capacity for 255 tons of fuel, delivered the following endurance.

Knots	Tons / hour	Endurance (hours)	radius (nm)
14	1.8	133	1,862
16	2.2	109	1,744
18	2.8	85	1,530
20	3.4	70	1,400
22	4.5	53	1,166
24	5.5	43	1,032
26	7.0	34	884
28	8.5	28	784
30	10.5	22	660

Thornycroft M

The ships' capacity for 275 tons of fuel, delivered the following endurance.

Knots	Tons / hour	Endurance (hours)	radius (nm)
14	1.6	162	2,268
16	2.0	130	2,080
18	2.4	108	1,944
20	3.2	81	1,620
22	4.2	62	1,364
24	5.6	46	1,104
26	7.0	37	962
28	9.0	29	812
30	11.5	22	660

Armament

4-in Guns

Their three 4-in Q.F. Mark IV guns on P IX mountings on the centre line were just as in the preceding "L" class destroyers and the final seven of the Acasta class. There were 120 rounds per gun: 36 common, 84 lyddite, an an additional 19 practice rounds.

The mounting could elevate 20 degrees and depress 10 degrees, but its sight could only elevate 15 degrees and the range dial was actually only graduated to 12.5 degrees (7,900 yards). "This was soon remedied by the supply of additional sight strips graduated to the extreme range of 10,200 yards."

These gear-worked sights had gearing constants of 26.66 and range dials for 2200 fps, and 1-in aiming rifle. MV could be corrected by a cam pointer allowing for a decrease to 2000 fps.

Unlike some P IX sights, these were not F.T.P. sights.

The midship gun was supplied with ammunition from the forward stores.

The deflection gearing constant was 52.6 with 1 knot equal to 3.18 arc minutes, corresponding to 2200 fps at 2000 yards. Drift was corrected by inclining the sight about pivot pins 2 degrees.

The layer's telescope sight line was 12.5 inches above the bore, and 21.45 inches left. The trainer's telescope sight line was 12.5 inches above and 17.4 inches right. Open sights were 13.3 inches above the bore and 24.35 inches left for layer and 20.3 inches right for trainer.

The sight had a temperature correcting scale plate and a "C" corrector.

The layer had an open sight. The trainer's sight could be used as a free sight with a counterweight.

During the war, some of the ships were required to land their aft gun to accommodate depth charges.

Other Guns

They may have carried one (later two) 1-pdr H.A. guns (later 2-pdr) as well as 4 mines on the upper deck. The first six ships were to complete with H.A. pompoms, and the others to receive theirs as they became available.

By 1920, some or all had one 2-pdr pompom for air defence.

Torpedoes

As in the preceding class, they had two twin 21-in tubes on the centre line enjoying 50 degree arcs centered on the beam.

Other Weapons

Depth charges were added to most destroyers, necessitating that some land their aft gun to accommodate the outfit.

Fire Control

Range and Order Instruments

By the end of 1915, at least, these ships had or were to be provided a range and order data system similar recent Barr and Stroud patterns.

The scheme placed the combined transmitter on the forebridge, and a combined receiver near the sightsetter position of each gun. Ranges from 0 to 9900 yards in increments of 100 yards, and orders were "Independent", "Control" and "Fire" with illuminated indicators and a red indicator on the receivers to signal loss of power from the battery pack located below decks.

Alterations

By November 1918, Prince and Meteor were fitted to carry 38 mines. The torpedo tubes and guns removed when the mines were shipped could be placed back aboard with enough notice.

See Also

• Medea Class Destroyer (1914)
• Wikipedia

Bibliography

• Gray, Randal (editor) (1985). Conway's All the World's Fighting Ships 1906–1921. London: Conway Maritime Press. (on Amazon.com and Amazon.co.uk).
• Admiralty, Technical History Section (1920). The Technical History and Index: Alteration in Armaments of H.M. Ships during the War. Vol. 4, Part 34. C.B. 1515 (34) now O.U. 6171/20. At The National Archives, Kew, United Kingdom.
• March, Edgar J. (1966). British Destroyers: A History of Development, 1892-1953. London: Seeley Service & Co. Limited. (on Bookfinder.com).