Philippine Marines deploy World War II Bofors 40mm anti-aircraft gun during combined exercise with the US.

As noted by Aaron-Matthew Lariosa on May 2, 2025, during the ongoing Balikatan 2025 joint military exercise, a 40mm Bofors L/60 anti-aircraft autocannon was observed in active use by the Philippine Marine Corps during a counter-landing live-fire drill in Rizal, Palawan. The system, originally used aboard a Second World War-era destroyer, has been mounted on a custom land carriage produced by the Philippine Marine Corps. This specific model is a 40×311 mm L/60, not the later 40×365 mm L/70 variant. Images show this gun in action during the drills, positioned beside a U.S. Marine Corps MADIS (Marine Air Defense Integrated System) vehicle, illustrating a notable technological contrast.
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During the ongoing Balikatan 2025 joint military exercise, a 40mm Bofors L/60 anti-aircraft autocannon was observed in active use by the Philippine Marine Corps during a counter-landing live-fire drill in Rizal, Palawan. (Picture source: US DoD)

Balikatan 2025, the 40th iteration of the U.S.-Philippines joint military drills, began on April 21 and will continue until May 9. The exercise includes participation from over 14,000 troops from the Philippines and the United States, as well as forces from Australia and, for the first time, Japan. Observers from additional countries are also attending. The exercise focuses on interoperability and coordination across air, land, sea, cyber, and space domains. It involves Combined Joint Logistics Over-the-Shore operations, humanitarian civic assistance activities, and command-and-control drills. This year’s scenario includes a "Full Battle Test," which simulates integrated combat operations among allied forces.

Among the key training events was a coastal defense exercise in Palawan, where Philippine Navy vessels—including BRP Lolinato To-Ong (PG 902), BRP Domingo Deluana (PG 905), and three multipurpose assault craft—used cannons and Spike-ER missiles against a maneuvering Hammerhead unmanned surface vessel. The U.S. Army’s 1st Multi-Domain Task Force deployed HIMARS (High Mobility Artillery Rocket Systems), transported via C-130 aircraft and landing craft from Subic Bay, to the western side of Palawan through jungle terrain. These units fired six training rounds at sea-based targets. According to Lt. Col. Ben Blane, commander of the task force’s Long-Range Fires Battalion, the exercise aimed to demonstrate land-based precision fires in support of territorial defense. Australian Javelin anti-tank missile teams and Philippine forces engaged with small arms, anti-tank rockets, and crew-served weapons.

The exercise also features deployments of U.S. systems to the Philippines for the first time, including the Typhon missile system and the Navy-Marine Expeditionary Ship Interdiction System (NMESIS). These platforms were stationed in strategic areas such as the Batanes Islands, located near the Luzon Strait. The U.S. Army also conducted live-fire testing of High-Powered Microwave (HPM) weapons designed to disable unmanned aerial systems. A planned ship-sinking drill was canceled after the target vessel sank prematurely due to sea conditions. Other scheduled events continued, including a maritime strike exercise off Western Luzon in the West Philippine Sea. The exercises occur amid increased tension between China and the Philippines over maritime jurisdiction in the South China Sea. In recent weeks, both nations have conducted competing drills near sandbars around Thitu Island and Subi Reef. U.S. Pacific Air Forces and Marine Corps aviation units, including Clark-based F/A-18 Hornets and a B-1B bomber, were involved in these broader operations.

The L/60 entered global export markets in 1932 and was used by at least 18 countries by the beginning of World War II, becoming one of the most widespread anti-aircraft guns of the conflict. (Picture source: US Army)

The Bofors 40mm L/60 is a medium-caliber anti-aircraft autocannon designed by AB Bofors in Sweden in the early 1930s. First entering service in 1934, the gun was designed as an intermediate anti-aircraft system, bridging the gap between smaller rapid-fire guns and larger long-range artillery. The L/60 uses 40×311 mmR shells, each weighing approximately 0.9 kg. It has a barrel length of 2.25 meters, muzzle velocity between 850 and 880 meters per second, and a maximum effective range of 7,160 meters. It can fire 120 to 140 rounds per minute depending on the elevation angle. The gun is mounted on a carriage weighing 522 kg and can traverse 360 degrees and elevate from -5° to +90°. It uses an automatic extraction system with a vertical sliding-wedge breech and a cam-operated recoil-powered autoloader.

The L/60 entered global export markets in 1932 and was used by at least 18 countries by the beginning of World War II. It became one of the most widespread anti-aircraft guns of the conflict, used by Allied powers including the U.S., the UK, and the Soviet Union, as well as some Axis countries such as Germany and Hungary. The U.S. Army designated its version as the M1. It was mounted on various platforms, including the M19 Gun Motor Carriage and M42 Duster, and deployed on naval vessels, aircraft, and in static positions. The U.S. Air Force also installed the L/60 on AC-130 gunships. In the postwar period, the L/60 was gradually replaced by the more powerful 40mm L/70 variant, adopted by NATO in 1953. However, large numbers of surplus L/60s remained in use into the 1980s and beyond.

In terms of production, Chrysler Corporation manufactured 60,000 L/60 guns and 120,000 barrels during World War II. Their engineering division had to convert Swedish blueprints from metric to imperial measurements and redesign components to enable industrial mass production. Amplex, a Chrysler subsidiary, produced sintered metal parts to reduce cost and production time. The U.S. Navy adopted multiple configurations including single, twin, and quadruple mounts. Later versions integrated radar fire control, including the STAAG (Stabilized Tachymetric Anti-Aircraft Gun) system, though it was eventually removed due to maintenance complexity. The U.S. Navy phased out the L/60 in favor of 3-inch/50-caliber guns due to the limitations of the 40mm round against high-speed aerial threats and its incompatibility with VT proximity fuzes.

The last known U.S. military use of the L/60 occurred in 2020 when it was removed from the final AC-130U gunships. (Picture source: US DoD)

The version seen in Balikatan 2025 appears to be a naval L/60 removed from a destroyer and retrofitted by the Philippine Marine Corps for land-based use. This adaptation is consistent with previous patterns of resource use within the Philippine military, particularly given the high number of global surplus L/60 systems. Though no longer suited for modern air defense roles, the gun may be used in a coastal defense capacity against slow or unarmored surface threats. Similar custom uses have been reported in other countries that retained the L/60 beyond its standard service life, including Indonesia, Paraguay, Brazil, and Taiwan. In Canada, surplus L/60s were reactivated as main armament on Kingston-class vessels in the 1990s. The last known U.S. military use of the L/60 occurred in 2020 when it was removed from the final AC-130U gunships.

The gun's development began in the late 1920s when the Swedish Navy requested a replacement for the Vickers 2-pounder. Bofors engineers based their design on a modified 57 mm semi-automatic naval gun. Early prototypes revealed issues with shell feeding, which were resolved by redesigning the loading mechanism to eject spent casings rearward and automatically insert new rounds. Krupp, which acquired a one-third share in Bofors, modernized the company's metallurgy during this period. Production of the finalized version began in 1934. The gun became the standard medium anti-aircraft weapon for several countries and was produced under license in Poland, Norway, India, Hungary, and elsewhere. Variants included retractable submarine mounts (L/43), and modified self-propelled versions. A lighter carriage developed in Poland was later adopted by the UK. British versions also included computerized fire control with the Kerrison Director and later the simplified Stiffkey Sight. The RAF Regiment used L/60s for airfield defense through the end of World War II.

Captured and licensed versions were also used by Germany, Hungary, and Japan. German forces designated the weapon as the 4 cm Flak 28 and employed it aboard cruisers, minesweepers, and fast attack craft. The Japanese Type 5 was developed from captured L/60 units. During the Cold War, the gun remained in service with several NATO and non-aligned nations, including in the Falklands War, and was later retired by most Western navies. In the Philippine context, its continued use during Balikatan 2025 occurs in a multinational training environment that includes newer U.S. systems like Typhon, NMESIS, and HPM weapons.