Naval News reports,

Following the trend of U.S. Navy ‘containerized’ solutions for various platforms, BAE Systems is pitching its Bofors 40 Mk 4 as another containerized system for counter-UAS, counter-USV, and point-defense missions. The gun was shown for the first time at Sea Air Space 2025 as part of a broader effort to introduce the gun and its ‘3P’ all-target ammunition to the U.S. audience.

The gun is certainly interesting, but we have looked at the system before. Perhaps the biggest news from the video is that the Navy is seeking palletized weapon systems. Potentially any 8×20 or 8×40 foot clear deck space could become a weapon station.

Presumably the Navy is thinking about arming merchant ships and MSC logistics ships that are currently essentially unarmed, but Coast Guard vessels may benefit as well.

The BAE Bofors 40mm Mk4 

BAE Bofors 40mm/70 mk4

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.

Other than small arms, the Coast Guard only uses weapons that are in the US Navy inventory so, unless the Navy adopts it, the following comments are just speculation. For what it is worth, I’ll offer my opinion.

Compared to the 76mm and 57mm, the 40mm has a shorter range, and no guided or extended range projectiles, as are now available for the 76mm and to a lesser extent the 57mm. For that reason, the 40mm is no substitute for the larger guns even though it does have a higher rate of fire.

The 40mm might be considered a substitute for the Phalanx CIWS. It weighs about half as much, and shoots much further. The British apparently think it can be used as a CIWS; they are putting two on each of their Type 31 frigates. The Italians used 40mm guns as their CIWS until they started using the Strales 76mm with DART ammunition in a much expanded CIWS role. The SeaRAM system should also be considered an alternative to Phalanx or the 40mm. It looks like a more likely candidate for large cutters. The 25mm Mk38 installation planned for the OPC appears to have an extremely restricted field of fire. Replacing it with the an elevated 40mm might help. SeaRAM would improve capabilities immensely.

The 40mm could be an alternative to the 25mm Mk38 mount currently on the Webber class WPCs, if the ships can take the extra 3200 pounds–guns as large as 76 are frequently seen on similar sized vessels–68% more range (13,670 yards (12,500 m) vs 7,450 yards); more than 5 times larger projectile (2.15 lbs. (0.975 kg) vs 0.406 lbs.); a 50% higher rate of fire (300 vs 200) and air bust ammunition. On the other hand we could get similar capability by adding small missiles like APKWS, Hellfire or JASM.