Explosive Shot

Lore & Background

The mine shell relies on inflicting damage primarily through the blast (pressure wave) alone, rather than the higher fragmentation but less blast provided by standard high-explosive shells. The specific effect, in German called Minenwirkung, in Swedish minverkan, lit. 'mine action', is defined by the Swedish Armed Forces as 'the pressure action from an encased explosive charge'. The effect is desirable when attacking non-reinforced and non-armoured targets such as brittle brick or concrete, and aircraft skin, as these are relatively easy to penetrate and do not need to be attacked by heavy, hard projectiles, but are tough enough to maintain their structure despite being pierced by shellfire and fragmentation. The larger explosions generated by mine shells are more efficient at inflicting damage on such targets than the greater kinetic impact but smaller detonations delivered by conventional rounds.

In Their Own Story

During World War II, mine shells came into use originally by Germany for small-caliber (initially 20 mm) automatic weapons, both to arm the Luftwaffe's fighter aircraft and for flak. This was an innovation, as prior to this mine shells had only been constructed in large calibers. In the late 1930s, the Germans began to pay attention to shortcomings during the trials of the 20 mm MG FF cannon. Its conventional high-explosive rounds were judged unsatisfactory in the anti-aircraft role. As a result, the German air ministry, the Reichsluftfahrtministerium, or RLM, ordered the development of mine shells for the 20 mm MG FF cannon in 1937. To make such shells in 20 mm caliber, German ordnance engineers developed a round made from high-quality drawing steel, manufactured in the same way as cartridge cases. These new 20 mm mine shells were first used against the RAF in 1940, and proved highly successful. The 20 mm mine shells used in MG FF/M cannons (and later in the MG 151/20) both had a 17 g HE filling (compared to the 4.5–6.5 g of the original MG-FF), while British and American autocannon shells of the same calibre, markedly heavier, could carry only 10–12 g.

Reader's Guide

To achieve the mine shell effect, shells have very thin shell walls, leaving more room for explosive filler, at the cost of generating lighter and less damaging shrapnel. Shells for use against thicker targets, such as brick or concrete walls, often use a delayed action fuze allowing them to penetrate a wall before exploding, forcing larger pieces of the targets to break loose. An additional advantage is that, as explosives are less dense than metal, the projectiles weigh less, giving them higher muzzle velocity than heavier shells and generating less recoil. Less desirably, the lighter shell has less momentum, and consequently shorter range. The lower recoil also makes them unsuitable to be fired from a gun with a recoil operated or advanced primer ignition mechanism suitable for heavier standard shells. This forced Germany during World War II to develop a special variant of the 20 mm MG FF cannon to fire mine shells, subsequently becoming the 'MG FF/M' (for Minengeschoß). Mine shells are often made longer than other shells of the same caliber, to increase both the weight and the explosive payload.

Did You Know?

• The word 'mine' in 'mine shell' originally referred to mining tunnels used in siege warfare to collapse fortifications, not land mines or naval mines.
• The 20 mm mine shells used in the MG FF/M cannon had a 17 g HE filling, compared to only 4.5–6.5 g in the original MG-FF round.
• The Swedish Armed Forces define 'mine action' (minverkan) as 'the pressure action from an encased explosive charge'.
• The German R4M air-to-air rocket's name stood for 'Rakete, 4 Kg, Minenkopf' (Rocket, 4 kg, Mine-head).
• The formal British military term for mine munition is 'High Capacity' (HC), with mine shells called 'High Capacity High-Explosive' (HCHE).