 HMS M21
|
| Class overview |
|---|
| Name | M15 class |
| Operators |  Royal Navy |
| Preceded by | Gorgon class |
| Succeeded by | M29 class |
| In service | 1915–1959 |
| Completed | 14 |
| Lost | 4 |
| General characteristics |
|---|
| Type | Monitor |
| Displacement | 540 tons |
| Length | 177 ft 3 in (54.03 m) |
| Beam | 31 ft (9.4 m) |
| Draught | 6 ft 9 in (2.06 m) |
| Propulsion |
- 2 shafts
- Triple-expansion
- 800 hp (600 kW)
- 4 shaft
- Bolinder 4-cylinder semi-diesel
- 640 hp (480 kW)
- 4 shafts
- Campbell 4-cylinder paraffin engines
- 560 bhp (420 kW)
|
| Speed | 11 knots (20 km/h; 13 mph) |
| Complement | 69 |
| Armament | |
The M15 class comprised fourteen monitors of the Royal Navy, all built and launched during 1915.
Design
The ships of this class were ordered in March, 1915, as part of the Emergency War Programme of ship construction. They were designed to use the 9.2 inch Mk VI gun turrets removed from the Edgar class and the Mk X turrets held in stock for the Drake-class and Cressy-class cruisers. This resulted in the first four of the class, which were built by William Gray & Company of Hartlepool, receiving the Mk X mounting. The remaining ten ships, all built by Sir Raylton Dixon & Co., Middlesbrough, all received the Mk VI mounting.
During September 1915, the 9.2 inch guns of HMS M24, M25, M26 and M27 were removed for use as artillery. These were replaced by 7.5-inch guns. M24 and M25 received the spare guns reserved for the recently sunk pre-dreadnought battleship Triumph, M26 received one of Swiftsure's spare guns. M27 received 6-inch (M27) guns.
M21 and M23 also had their 9.2-inch gun removed in 1917, receiving 7.5-inch guns from the decommissioned pre-dreadnought Swiftsure.
The class used a mixture of propulsion methods. M21 and M22 were fitted with conventional triple-expansion steam engines, M24 was fitted with four-cylinder paraffin engines, and the remainder received Bolinder four-cylinder semi-diesel engines.
Admiral Reginald Bacon, who had commanded several of the M15 class in the Dover Patrol, wrote about his experiences with the ships of the patrol in 1919. While generally positive about the performance of the design, he noted that they had a tendency to roll, using a specific occasion with M25 as an example;
- "The M25, while in the mouth of the Thames at anchor, rolled 180 degrees in ten seconds - that is, she made two complete rolls of 45 degrees each way, each occupying only five seconds."
Service
M25, M26, M27 and M28 served in the Dover Patrol from 1915 to 1918. The remainder served in the Mediterranean from 1915, with M23 joining the Dover Patrol in June 1917 and M21 in October 1917.
As part of the intervention into the Russian civil war M23, M24, M25 and M27 served in support of British and White Russian forces in the White Sea in May to September 1919.
M22 was converted to a minelayer in 1920, whilst M23 became a drill ship, surviving until 1959.
