Dual purpose gun

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The Mark 37 Model 6 5-inch dual purpose gun on display at the National Museum of the Pacific War. The gun had a range of over 6 miles and could fire 22 rounds a minute.

A dual purpose gun is a naval artillery mounting designed to engage both surface and air targets.

Description

Second World War-era capital ships had four classes of artillery: the heavy main battery, intended to engage opposing battleships and cruisers (356 mm (14 inch) or greater); a secondary battery for use against enemy destroyers of 127 to 155 mm (5 to 6.1 in); heavy anti-aircraft guns of 90 to 127 mm (3 to 5 in), which could create barrages to knock out aeroplanes at a distance; finally, light rapid-fire anti-aircraft batteries (A/A) to track and bring down aircraft at close range. The light A/A was dispersed throughout the ship and included both automatic cannons (20–40 mm) and heavy machine guns.

During World War II, the US Navy, Royal Navy, the French Navy and the Imperial Japanese Navy combined the secondary battery with the heavy anti-aircraft guns, creating a dual-purpose secondary battery. They discarded the dedicated, anti-ship secondary batteries altogether, because a battle-line fleet would be screened against cruiser and destroyers most of the time. Also, it was deemed unlikely that a battleship would be simultaneously facing both rushing destroyers and aircraft, and it would take up too much space to have separate types of guns to deal with both threats. Rather, they replaced them with turret-mounted dual purpose guns that could be used against both aircraft and ships. The space saved from combining the two types of guns added to simplification of supply, increased deck armour coverage, stowage of other equipment, a larger light anti-aircraft battery, and other needs. This arrangement was seen more efficient, and was deemed adequate to meet anti-surface and anti-aircraft needs under most circumstances.

The Kriegsmarine, in a practice similar to the Italian and Soviet navies, adopted a mixed-calibre secondary battery, with dedicated anti-ship guns, coupled with smaller-calibre heavy anti-aircraft batteries, instead of adopting dual-purpose secondaries like the British or Americans. Both navies were concerned of close-range torpedo attacks from enemy (in particular, French) destroyers and torpedo boats, and considered the more powerful, larger calibre anti-ship secondaries a must. The French Navy used a mixed-calibre system, as well, but their secondary battery was dual-purpose. This tended to complicate ammunition supplies and render certain armament useless in some situations.

Dual purpose guns are designed as a compromise between the heavy main armament of a surface combatant and dedicated anti-aircraft guns. Usually of a mid-range caliber, the gun is heavy enough to prove useful against surface targets including ships, surfaced submarines, and land targets. However, it is compact enough to fit into a mounting capable of good traverse and high elevation, as well as being capable of a high rate of fire, allowing it to successfully engage air targets at all angles. For example, a Royal Navy battleship of the King George V class had sixteen QF Mark I 5.25-inch (133 mm) guns that could engage either enemy ships or high level aircraft, as necessary, but was found lacking in the AAA role due to its limited elevation, and slower than expected rate of fire due to the larger shells it fired. French experience on the Richelieu class battleships with large calibre dual-purpose artillery was similar. On the other hand, the US Navy's 5" DP guns were considered highly successful.

Dual purpose guns, often abbreviated to DP guns, were originally designed as a secondary armament for large surface ships such as cruisers and battleships to complement their heavy main armaments. Later, such guns began to be added to smaller vessels as their primary gun armament, and with the progression of ship design away from heavy caliber guns, today nearly all main gun armaments are of dual purpose nature.

Most DP mounted guns have calibers in the range from three to five inches.

In British service the term HA/LA for "High Angle/Low Angle" was used.

See also

• List of artillery