Bouncing bomb

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Bouncing bomb: Upkeep and the Dambusters Raid

A bouncing bomb is a weapon designed to skip across water toward a target, so it can hit underwater and explode beneath it. It was created by British engineer Barnes Wallis in World War II. The Upkeep version was the large bomb used in the famous Dambusters raid.

How it worked
- The bomb was dropped from a bomber at about 60 feet above the water, traveling at around 232 mph.
- It was given a strong back-spin (about 500 rpm) to help it bounce across the surface.
- After several bounces, the bomb would strike a dam underwater, sink, and explode at a preset depth to cause the most damage.
- The explosion relied on an underwater shock effect to crack the dam.

The Upkeep design
- The full operational Upkeep bomb weighed about 9,250 pounds (4,200 kg) with about 6,600 pounds (3,000 kg) of explosive Torpex.
- It carried a cylinder containing the explosive inside a spherical shell, and used hydrostatic pistols to detonate at about 30 feet (9 meters) underwater.
- A self-destruct fuse could trigger if the bomb didn’t detonate in time.
- The system also included mechanisms to release and stabilize the bomb from the aircraft and to ensure the correct height and distance before release.

Development and context
- Wallis’s early ideas described a weapon that could be dropped to bounce on water and explode underwater, drawing on the “bubble pulse” effect to maximize damage.
- Two main versions were developed: Upkeep for dams and Highball for ships. A third idea, Baseball, was planned but never produced.
- Testing occurred at Chesil Beach and Reculver, using modified bombers to refine balance, spin, and release.

The raid: Operation Chastise (May 1943)
- On the night of 16/17 May 1943, 19 Lancaster bombers attacked German dams in the Ruhr Valley using Upkeep.
- Two dams were breached, causing extensive flooding and damage.
- British losses were high: eight aircraft did not return, and many aircrew were killed or captured (about 53 aircrew casualties in total).
- The breaches disrupted German industry and transport for a time, but the long-term impact on the war is debated.

Aftermath and legacy
- Upkeep was not used again in active operations.
- Development of Highball continued for a time, but it was never used in combat.
- Prototypes and inert bombs from both Upkeep and Highball have been recovered and preserved at museums, and some Highball prototypes have been recovered from underwater sites.
- In 2011, researchers re-created a bouncing bomb concept for a modern demonstration, testing a replica bomb in a controlled setting.

Key facts
- Code name: Upkeep
- Type: Large bouncing bomb designed to detonate underwater
- Designer: Barnes Wallis
- Manufacturer: Vickers-Armstrongs
- Carrier aircraft: Avro Lancaster (modified for Upkeep)
- Weight: 9,250 pounds (4,200 kg); explosive fill: 6,600 pounds (3,000 kg) of Torpex
- Length/width: about 60 inches by 50 inches (1.52 m by 1.27 m)
- Speed and spin: 240–250 mph (390–400 km/h); back-spin around 500 rpm
- Release height and distance: ~60 feet above water; 400–500 yards range
- Detonation: hydrostatic fuze set for about 30 feet underwater
- Operational result: Two dams breached during Operation Chastise; significant flooding and civilian casualties; eight aircraft failed to return
- Later use: Upkeep not reused; Highball developed but not deployed operationally; Tallboy and other bombs used later in the war.