The 5 inch Mk 45 is a naval gun turret of US origin. It was developed in the 1960's by United Defense as a lighter alternative to the earlier Mk 42 turret. The Mk 45 is the smallest 5 inch/127mm gun turret in the world and can be considered a direct competitor to the Italian 127mm Compatto. The Mk 45 is a lighter and easier to install design while the Compatto has a higher rate of fire. Both guns use the same US standard 5 inch ammunition.