Suffix designations:
   CLV:  Controlled Low Velocity
   CHV:  Controlled High Velocity
   CHV(U):  CHV with modification to latch locking crank
   ALV:  Automatic Low Velocity
   AHV:  Automatic High Velocity
   CHV^W and AHV^W:  CHV and AHV with modified cooling jackets to allow water circulation

There were also right and left hand inner and outer guns (indicated by the suffixes RHI, LHI, RHO and LHO), the differences being in the ammunition feed.  In outer guns and in upper guns in quadruple mountings, the connecting block in the gun - which took the barrel, buffer cylinders and ejector tube - was lengthened by 13 inches (33 cm) to allow the ammunition feed for inner and lower guns to pass through.

Automatic Firing Gear:  115 rounds per minute

1) These weights probably do not include the cooling water.  Only CHV^W and AHV^W guns were fitted for water recirculation, other models had simple water jackets.  The common filler for these was a prominent funnel at the rear of the gun assemblies, as can be seen in the sketch of the Mark VII quad mounting shown on the additional pictures page.

2) Controlled Firing - In any multiple automatic weapon mounting, if each gun is allowed to fire on its own then they are all going to cycle at a slightly different rate.  This means that at some point they are all going to be firing simultaneously, causing obvious shock and vibration problems as well as creating a "gap" in the bullet stream.  An alternative to letting the guns fire freely is to synchronize them in some manner such that they fire sequentially and in a pre-determined pattern.  This was the path that the British chose for the multiple 2-pdr mountings, and the use of the cranked firing gear for these mountings ensured that the guns were synchronized - which the British for some reason called "controlled."  In other words, the cranked firing gear meant that all guns fired at the same rate and in a planned sequential order.  In the case of the quad mounting, the guns fired in pairs and this was probably the same for the octuple mounting.  In 1939, the British apparently concluded that the concerns of allowing the guns to fire freely was less of a problem for the octuple mountings than it was for the quadruple mountings and so changed the octuple guns so as to eliminate the "controlled" firing gear.

HE HV - 1.81 lbs. (0.82 kg)

HE HV - 2.87 lbs. (1.30 kg)

HE HV - N/A

1) Low Velocity type shells were first introduced in 1914.  The High Velocity type was introduced in 1938.  HE tracer does not appear to have been issued prior to 1942.  Norman Friedman in "US Destroyers" says that self-destructing ammunition was used, but I have found no evidence of this in official design documents.  It is possible that the tracer elements was used to self-destruct the projectiles.

2) The usual outfit was HE and HE tracer, but SAP and AP were issued to a limited number of ships.

3) Ammunition was supplied in 14-round steel-linked belts which could be hooked together.   Ammunition feed boxes held 140 rounds per gun for the octuple mounting, 112 rounds for the quadruple mountings and 56 rounds for the single mounting.

4) Complete breakdown of LV shell weight from "Q.F. High Explosive 2 pdr Mark II N Shell":

   Empty body:  1.45 lbs. (0.66 kg)
   Driving band:  0.875 oz (0.025 kg)
   Paint:  0.125 oz (0.0035 kg)
   Bursting charge:  2.5 oz (0.071 kg)
   Fuze No 131:  5.25 oz (0.15 kg)
   Total filled:  2 lbs. (0.9 kg)

Quadruple Mounts
   Mark VII
   RP 50 Mark VII*
   Mark VII*P

Single Mounts
   Mark VIII and Mark VIII* (hand worked)
   Mark XV (power worked)
   Mark XVI (power worked and used primarily by coastal forces)

Quadruple
   Mark VII*:  8.58 tons (8.7 mt)
   RP 50 Mark VII*:  10.00 tons (10.16 mt)
   Mark VII*P:  11.01 tons (11.19 mt)

Single
   Mark VIII:  1.78 tons (1.8 mt)
   Mark XVI and XVI*:  1.1 tons (1.1 mt)

RPC Mounts:  25 degrees per second

RPC Quad Mounts:  25 degrees per second
RPC Single Mounts:  40 degrees per second

1) The Mark V differed from the Mark VI by having a heavier carriage and different controlled firing gear.  Both were trained and elevated by a self-contained electro-hydraulic system powered by an 11 hp motor.  The later octuple mountings with motorized firing gear were introduced in 1939 and designated as Mark VA and Mark VIA.  As originally introduced, guns lacked shields and flash hiders, these were added during the war.

2) Mountings capable of firing the HV projectiles are indicated by the star (*) in their designations.

3) RPC and water cooling jackets were added to the Mark VIA* mountings at the same time.

4) USN Mark 14 gyro sights were added to some quad mountings in 1945 as an anti-kamikaze measure, mainly for ships intended for the Pacific area of operations.  At least the battleships Anson and Duke of York and the carrier Implacable were so fitted.

5) The Mark VII and Mark VII* were hand elevated and trained.  The Mark VII*P was a late war quadruple mounting with self-contained power that had a dual joystick control.  RP 50 Mark VII* mountings also had local joystick controls.  Power control was still controlled by the hand cranks, which allowed a simpler "hand clutch" return to manual operation in the event of a loss of power.  The crew for the quadruple mountings consisted of eight men, starting with the gun captain, who was in general charge and operateed the firing clutch lever.  The remainder of the crew were the gunlayer, trainer, ammunition feed numbers and loaders for right and left guns.

6) The single Mark XVI and XVI* mountings were derived from the twin 20 mm Oerlikon Mark V mountings.  The Mark XVI was hydraulically powered by an off-mounting driven by the main or auxiliary engines on coastal craft.  In the Mark XVI*, an electric motor was provided to drive the pump.  Both versions had scooter control.  Some of the Mark XVI* mountings were fitted with USN Mark 14 gyro sights and used on the carrier Ocean and some cruisers and destroyers assigned to the Pacific fleet in 1945.  Elevation was restricted compared to other 2-pdr mountings as the position of the elevating trunnion axis was lower, due to the smaller nature of the Oerlikon guns.

7) At the start of the war, octuple mountings had been installed on battleships, battlecruisers, some 8-inch (20.3 cm) cruisers, the AA cruisers Coventry and Curlew, and the minelayer Adventure.  The largest number at this time was four Mark VI mountings on both Warspite and Ark Royal.  By the end of the war, there were as many as eight octuple mountings on the King George V class battleships while the battleship Nelson, the cruiser Sussex and the fleet carriers carried up to six octuple mountings.

8) Quad mountings were introduced for smaller ships in 1935-36 and was first successfully tried on the destroyer Crusader (H60).  By September 1945 there were six RP 50 mountings on each of the Colossus class carriers, the cruisers Glasgow and Liverpool and six Mark VII*P mountings on the battleships Duke of York, Anson and Howe.  Destroyers starting with the "Tribal" class and up to one of the "S" war emergency class had a single quad mount installed amidships.  Some earlier destroyers had a single quad mount fitted during the war.