Up-arm the fleet with the 21st century evolution of your grandfathers gun

...they've made the Bofors 40mm great again

Back in the first week of May, we had the second edition in what has become a series about what options exist on the table to get additional weapons on ships: Yes, Reality Demands More Guns, Larger Guns, Everywhere. It was a follow-up to March’s Up-arm the Fleet? With What?

A principal concern I have was outlined in a previous article in November 2024, Arm the Auxiliaries.

If you are new to the issue, give the above a read and then come back.

In addition to the primary concern, the secondary concern is our existing ships that are already armed, but do not have the best mix of weapons to address the new reality—the many cheap, unsophisticated, but deadly swarming threats now appearing both in the air and on the surface.

For generations, the threat was always the few, exquisite, sophisticated, and fast. We built those, and built to defend against them. That threat is still there, but now we have new threats that cannot be ignored.

Due to structural integrity, moment arms, survivability, and a whole host of engineering issues—you just can’t willy-nilly go about putting weapons all over the place.

You do have options ready to go, but in the previous posts I failed to mention an old girl who is having quite a renaissance—and soon we will be seeing a lot more of.

You naval history nerds are going to get all misty-eyed on me, but we’ll just have to work through it.

Ladies and gentlemen, find a little topside space, and welcome onboard the Bofors 40 Mk4 Naval Gun.

The low weight and compact Bofors 40 Mk4 gun system with its high rate of fire and ability to switch between optimized ammunition types – including the intelligent 40mm 3P all-target ammunition – provides high survivability and tactical freedom at all levels of conflict.

…

Control:

• Computer-controlled burst pattern

• On-mount muzzle velocity radar

• Remotely-operated with gyro-stabilised local control backup

Firing:

• 6-mode programmable all-target ammunition

• Short firing sequences: 300 rounds per minute.

• Superb accuracy

• 100 rounds ready to fire with the possibility to shift between different types of ammunition

• Air burst capability for small boat defence

That 6-mode capability is…something.

The incoming Type 31 frigate for the Royal Navy, and a few export customers, has two of these in addition to its 57mm main mount (NB: really should be at least 76mm, but you know my biases).

Look where these are located on this ship. It shows some flexibility on where these can be installed on other ships.

There is so much confidence in the modern evolution of this almost century-old weapon that the Type 31 does not need a CIWS-SeaRam etc.

Our friend Chuck covered it a bit over a year ago:

The 40mm/70 has a long and successful history. The earlier 40mm/56 was the best medium caliber anti-aircraft gun of WWII. The air cooled single 40mm/56 mount was used on Coast Guard cutters post war including 125 foot Active class cutters and B-class 95 foot Cape Class patrol boats. Twin and quad water-cooled mounts were used on larger cutters e.g. 255s, 311s, 327s, and icebreakers. The US Navy moved from the 40mm to the 3″/50 at the end of WWII because it did not have room for a proximity fuse. Miniaturization now allows the 40mm to have the same sophisticated sort of 3P fuse available for the 57mm Mk110.

Our ships need more defensive weapons, and due to their flexibility and utility, guns will be a major part of that.

When the next Great Pacific War comes, we will put weapons anywhere we can on every kind of ship you can think of—all while cursing those who spent decades ignoring this requirement.

This clearly should be in the mix. If we were smart, especially with our unarmed auxiliaries, we would not wait for war to start doing this.

If you review what Navy Lookout and BAE Systems outline about its footprint requirements, you can get an idea about where we could put them.

• Turret Diameter: The base support ring is approximately 1,850 mm (72.8 inches) in diameter, which evenly distributes recoil forces. [1]

• Height: The above-deck mount has a low profile standing under 2 meters (78.7 inches) tall. [1]

• Deck Penetration: Because the gun stores up to 100 rounds inside the turret itself, it can function purely as a “bolt-on” system with zero deck penetration. If you choose to configure it with an under-deck penetration for a larger magazine, the penetration is only about 590 mm (23.2 inches). [1, 2, 3, 4]

• Weight: Weighs approximately 2,300 kg (5,100 lbs) excluding ammunition. A fully loaded mount with 100 ready-to-fire rounds weighs about 2,500 kg (5,500 lbs). [1, 2]

To end things up, British Naval History crew at YouTube have a great summary.

All it takes is for people to stop appreciating the problem and instead, take action.