The 1950s was a fascinating period in the development of military technology since it was a time of transition in many ways, including from piston-engined combat aircraft to supersonic jets, and from big guns to missiles. With the development of the atomic bomb and fast bombers to carry it, national air defence had a high priority. Fighter jets were the main weapons, but an inner layer of defence was needed to deal with any bombers which got through. It was clear that anti-aircraft missiles were likely to be the future, but their performance was initially too poor to rely on them, so
Battle Flight contains a description of the various AA gun projects of the 1950s, including automated versions of the existing 3.7 inch guns, a 4.26/3.2 inch (108/81 mm) squeezebore gun (a barrel for which still survives), the exotic Green Lizard (a gun-launched guided missile carrying submunitions), and the Green Mace. The Green Mace project consisted of three different guns: prototype 4 inch and 5 inch rifled guns (102 mm and 127 mm), and the planned service 5.68 inch (144 mm) smoothbore gun. The projectile was to consist of a long, sub-calibre, fin-stabilised discarding-sabot HE shell, with a muzzle velocity of 6,000 fps (1,829 m/s). The 4 inch and 5 inch guns were built and tested in 1954 and 1955, achieving short-burst rates of fire of 96 rpm and 75 rpm respectively. Ammunition was fed from two rotary magazines, one on each side of the gun, which elevated with it (similar systems were used in the American Skysweeper 75 mm AA gun and in the French AMX-13 light tank). Each magazine contained 14 rounds, so would need frequent replenishing in action. The barrels were water-cooled. The gun systems, mounted on wheeled trailers, were massive; the 4 inch version weighed 28 tons while the ultimate 5.68 inch was expected to weigh 62.5 tons - but it was never built, the project being cancelled in favour of guided missiles in 1954, though test firing of the prototypes continued for several years.
I have examined a sectioned 5 inch Green Mace round at Shrivenham; the case measures 127 x 690R x 172 rim and although the headstamp is faint it clearly includes "5 INCH".
Meanwhile, Vickers had been developing an automatic 4 inch naval gun. This gun was based on an experimental land service "X1 Medium AA Gun" which was test-fired in 1956. This was not the same gun as the Green Mace, since it used a different loading system - through the gun trunnions and fed by a couple of fixed hoppers on either side of the gun holding 28 rounds each. The rate of fire was 40-50 rpm. The naval gun was designated Mark Q, the single-barrel mounting the Mark N(R) or Vickers Universal Mount. The gun was rejected by the Royal Navy, in part because of the lack of a water-cooled barrel, but it was sold to Chile to arm the two Almirante class destroyers.
The Mark Q gun was originally designed around the 102 x 730R x 150 ammunition used in the L45-calibre MK 19 (the Royal Navy's standard 4 inch gun at the end of World War 2), but before entering service was modified to take an L62-calibre barrel with a higher performance. One source states that the ammunition for the L62 measured 102 x 670R, which fits in nicely with the British round shown below, which measures 102 x 670R x 173. It also explains why this round has the following projectile markings: 102 MM QF HE 4" - putting the metric measurement first suggests a foreign customer. It therefore seems highly probable that this 4" round was used in the Vickers Mark Q gun in the Chilean destroyers.
However, this still leaves some unresolved matters concerning Green Mace ammunition. The problem is that "Green Mace" being an MoD code designation, it was never stamped on the rounds as far as I know.
The 4 inch round is said to be a version of the 4 inch Green Mace modified to fire a conventional HE shell. I have not seen any evidence that this round was used in Green Mace, but the fact that the rim diameter and overall round length are virtually identical to Shrivenham's 5 inch Green Mace indicates that there is probably a relationship.
The 5 inch Green Mace is a bigger problem: Dave Birkin measured the large case shown on page 2 at 127 x 984R x 200, which is substantially bigger than the 5 inch Green Mace round at Shrivenham. So which is the real Green Mace, or were two very different 5 inch rounds developed? Or could Dave's big case be a 5.68 inch [no, it wasn't!]? A further thought: the Royal Navy was interested in a very high-performance 5 inch L70 at this time – could it be for that?
If the strings of code letters which appear on some of these rounds (shown below) could be deciphered all might become clearer, but can anyone shed light on this?
The headstamp on the big 5" case above includes the following:
RLB 1952 DD2/52/401 D2/I/5998 5..N
The headstamp on the 4" includes:
1955 EQN D2/52/903 CODE/46/30/221
The projectile in the 4" case includes the following markings:
SL CJ509 102MM QF HE 4" D2L/CD210'E D2 52 804 AMEND 25 A 321 H H OFW 8/54
References:
ECRA Bulletins: 504-1; 535-16; 570-29; 571-19; 581-2; 605-8; 607-6
Battle Flight: RAF Air Defence Projects and Weapons Since 1945 by Chris Gibson (Hikoki, 2012)
The Vickers 4 inch Mark N(R) mounting, an article by Peter Marland in Warship 2013 (Conway, 2013)
Hi All,
