What are Dual-Purpose Guns?

what are dual-purpose naval guns

Dual-Purpose Guns

One of the biggest advancements to happen to warships during the Second World War was the introduction of dual-purpose guns. Effectively combining the roles of several weapon systems into one, the arrival of dual-purpose guns allowed ships to save weight and become even more lethal. In this article we answer the question of what are dual-purpose guns, how they came about, and what made them so effective.

What Are They?

what are dual-purpose guns
One of the first successful dual-purpose guns was the Japanese 12.7cm/50 Type 3 mounted in the model B turret. Fully enclosed and capable of elevating to 75 degrees, the weapon was revolutionary.

Prior to the introduction of dual-purpose guns, most capital ships were armed with four classes of guns. The first was the primary battery of heavy guns designed to engage battleships and cruisers. The second class consisted of smaller guns intended to fight smaller ships such as destroyers or torpedo boats. The third class consisted of heavy anti-air guns design to engage aerial targets at longer range. Lastly, the ship was equipped with light, rapid firing anti-aircraft guns that would intercept aircraft at extremely close range. This set up was standard on most capital ships  from the First World War until just before the Second World War. While having the benefit of allowing each gun to be tailored for a specific role, this arrangement was heavy and consumed valuable deck space.


In the late 1920s, the United States, the United Kingdom, France, and Japan all developed a new weapon the combined the secondary anti-surface battery with the heavy anti-aircraft battery. These were the first dual-purpose guns. They combined a round sufficiently heavy to harm light warships with a mounting that could elevate high enough to engage aircraft. This new arrangement saved thousands of tons in weight, simplified logistics, and freed up deck space for additional light anti-aircraft weapons.

What Did They Do?

Just as the name implies, a dual-purpose gun was intended to fulfill both the anti-air and anti-surface roles. The gun had to just heavy enough to be useful in the anti-surface role while also being small enough to fit in a mount capable of engaging aircraft. This size requirement often limited the gun to between 4.5″ (114mm) and 5.25″ (133mm) in its most common sizes. Smaller and larger guns were tried to varying degrees of success. More important than the gun, was the mounting that held it. A capable dual-purpose gun had to be able to elevate high enough to hit aircraft while also having the ability to traverse fast enough to track them. As aircraft got faster, the turret mounts had to also get quicker to effectively engage them. Some dual-purpose guns, like Japan’s 12.7cm/50 lost much of their effectiveness as the war went on as they could no longer handle the advanced Allied aircraft.

Where Were They Used?

what are dual-purpose guns
The battleship USS Washington. Her formidable battery of dual-purpose guns are seen amidships in this photo.

Dual-purpose guns, once their effectiveness was discovered, were quickly mounted on all manner of warships large enough to handle them. Dual-purpose guns were mounted on various destroyers, cruisers, battleships, and carriers. Destroyers often carried four to six guns while battleships could carry as many as twenty-four. Depending on the application, some ships carried fully enclosed turrets while others carried open mounts. Nations like the United States and Japan started the Second World War mounting Dual-purpose guns on the majority of all new ship construction. Other nations like Britain, were incapable of manufacturing the quantities of guns needed at the start of the war and mounted them only on capital ships and other important vessels. As the war went on Britain introduced newer models of guns and began equipping them on nearly all of their warships.

How Effective Were They?

Its typically thought that dual-purpose guns were vastly more effective to the older dedicated weapons. This isn’t always the case. They were relatively equal in performance compared to separate batteries of anti-air and anti-surface guns, it was the fact they saved so much weight that made them so effective. The value of saved weight and additional deck space was immense on a warships, especially in an environment where those things were already in short supply. The freed up space was available for additional anti-aircraft guns, newer electronics, or any other equipment. The fact that dual-purpose guns are still utilized today is a testament to their effectiveness.

Links and Other Reading Material

I hope you enjoyed the article. I am making it a point to write some smaller articles to appeal to more people. If you liked or disliked this new method, please comment in the section below or in the forum. Follow us on Facebook, Twitter, or Google + to keep up with all the latest articles.

Here are a few more articles for you to check out:

Read the article that started it all, the Iowa class battleships and why it was a departure from traditional battleship design.

Fellow Author Matthew J. Wright asks if nuclear propelled surface ships are still viable.






Chris Knupp

A student of military history, I am working to make history more interesting and accessible for everyone.



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