LAST OF THE DAM BUSTERS
The Hwachon Dam in South Korea is a concrete hydroelectric dam built by the Japanese on the North Han River. The Han River Hydroelectric Company began construction in July 1939 and the dam was completed in October 1944. A gravity dam 435m (1427ft) long, with a hydraulic head of 74.5m (244ft), fed from a catchment reservoir with a surface area of almost 39 square kilometres (15 square miles), its turbines are rated at 108MW.
During the Korean War, control of the dam and its associated power station were key objectives for both sides. The United Nations forces were concerned that the North Koreans would make tactical use of the dam, disrupting military operations downstream by the simple expedient of releasing spillwater through the dam’s sixteen sluice gates, leading to major flooding. Alternatively, the Chinese could try to cut the flow of water completely, enabling their troops to more easily ford the river and attack the UN forces. It was therefore felt vital to either capture the dam or damage its sluice gates. Destroying the dam itself was not considered an option, since this would, in fact, cause the flooding on a vast scale which the UN forces wished to avoid.
Already, at midnight on 8 April 1951, the Chinese Communist forces had opened crest spillways and released large quantities of water. The level of the Han River was raised by 4ft (1.22m), sweeping away one UN military bridge and forcing the dismantling of a second bridge to avoid its destruction. Accordingly, on 9 April the 7th Cavalry and the 4th Ranger Company were tasked with taking the dam and its environments. The 7th Cavalry advanced to within half a mile of the dam by 10 April, but were halted by two dug-in companies of Chinese troops. The next day they renewed the attack, while the Rangers and other troops tried to cross the reservoir in an amphibious assault. This latter effort made slow progress, not surprisingly, since only nine assault boats arrived, and only four of these had motors. As only one 155mm howitzer could actually range the dam, the attack was called off.
The onus for neutralising the spill gates shifted to American aviators. B-29 bombers tried to hit the dam but failed. Navy Skyraiders attacked with 2000lb (900kg) bombs and 11.5in Tiny Tim rockets, but again they failed. The steel sluice gates were 20ft tall by 40ft wide (6.1m × 12.2m), situated on the top of the dam beneath reinforced concrete frames. They were a small target which was difficult to hit.
Searching around for a solution, Skyraider pilots flying from the carrier USS Princeton (CV-37) wondered if they could torpedo the sluice gates. After all, the officially-stated aim of the Japanese aircraft carrier submarines of the I 400 class and their Aichi Seiran attack aircraft had been to block the Panama Canal by torpedoing the lock gates. It was recalled that Princeton carried several Mark 13 aerial torpedoes of the type used in the Pacific War, but there was no one on board who had ever tried to attach one to an aircraft. Digging through instruction manuals, the ordnance handlers were surprised to discover that the Douglas AS-4 Skyraider, nicknamed the ‘flying dump truck’ (many years before it earned its better-known nickname of ‘SPAD’ in Vietnam) actually had the connections to both carry and launch the Mark 13.
Luckily, three of the pilots aboard Princeton had actually practised dropping torpedoes years earlier, and they set to initiating five more pilots from Attack Squadron VA-195 in the special techniques involved. The attack by the eight torpedo planes, escorted by twelve Corsair fighters for AA suppression, was launched on 1 May 1951. Their aim was to destroy at least two of the sluice gates, blowing holes in the top of the dam which would allow a steady flow of water to pass.
Arriving over the target area, the Skyraiders broke into two-plane sections and began their runs. They intended to drop their torpedoes at a speed of 160 knots just 100ft (30m) above the surface of the reservoir. Six of the eight torpedoes struck on or near sluice gates. One of these was destroyed and a second one damaged. The dam was breached at both extremities, and the mission was deemed a success. Attack Squadron VA-195 took on the official title of ‘The Dam Busters’. The dam, which was later captured by UN Forces, remains in use today.
HM SUBMARINE SIDON
The explosion of an air flask, or even the open-air explosion of a warhead on deck, can cause serious damage, but is unlikely to lead directly to the loss of a large vessel such as a cruiser — unless an uncontrollable fire results. On the other hand, submarines are vulnerable to explosion of a torpedo mechanism inside a loaded tube, especially when the torpedo fuel is highly volatile hydrogen peroxide.
HMS Sidon was an ‘S’-class submarine displacing 990 tons submerged, commissioned in November 1944. On 16 June 1955 Sidon was alongside her depot ship HMS Maidstone in Portland. Her crew were preparing to test fire two 21in Mark 12 torpedoes, codenamed ‘Fancy’, for testing. Design of the Mark 12’s power plant was based on Second World War German technology, using high test hydrogen peroxide (HTP) as fuel. At 1825, the Mark 12 loaded in Sidon’s № 3 tube suffered a violent explosion, which ruptured the torpedo body, burst the tube and disrupted the two forward watertight bulkheads. Sidon listed to starboard and began to sink by the bows.
Twelve crewmen were killed in the explosion and seven seriously injured, but Lt Cdr Verry ordered the evacuation of the remainder of her crew via the aft and engine room escape hatches. Unfortunately, the medical officer on HMS Maidstone, Temporary Surgeon Lieutenant Rhodes, who had descended into the sinking submarine wearing a breathing apparatus he had not been trained to use, was overcome by the toxic fumes and also died.
The investigation determined that the engine of the Mark 12 had run hot, having accidentally started while still in the tube. Out of its water environment, it had over-speeded, creating high pressure in its fuel system. The HTP fuel line burst, spraying peroxide onto internal copper fittings, which caused it to decompose into oxygen and steam. The warhead itself had not exploded, but the expanding gases trapped in the torpedo body had burst it, sinking the submarine.