of heavy water produced during the German occupation, over , was destroyed with equipment critical to the operation of the electrolysis chambers. Although 3,000 German soldiers were dispatched to search the area for the commandos, all escaped; five commandos escaped by skiing to Sweden, two proceeded to Oslo (where they assisted Milorg), and four remained in the region for further resistance work. Resumed operation and Allied air raids The attack halted production for several months, although it did not permanently damage the Vemork plant. The plant was repaired by April; SOE concluded that a repeat commando raid would be extremely difficult, since German security was considerably improved. Almost as soon as production resumed, the USAAF began a series of raids on Vemork. The plant was attacked in November by a massive daylight bombing raid of 143 B-17 heavy bombers, which dropped 711 bombs. Although the raid caused extensive damage, at least 600 bombs missed the plant. On 16 and 18 November, 35 B-24 heavy bombers from the 392nd Bomber Group (based at Wendling, Station 118) extensively attacked the hydro-electric power station at Rjukan. The missions, the bomber group's longest, lasted and hours respectively. There was less need for ground assaults than a year earlier, since night bombing (previously unrealistic due to German air cover) was now an alternative. The Germans, convinced that air raids would result in further serious damage, decided to abandon the plant and move its remaining stocks and critical components to Germany in 1944. Sinking of the SF Hydro Knut Haukelid (the only trained commando in the immediate area) was informed of the German plan to remove the heavy water, and was advised to muster support and destroy the shipment. Haukelid recruited two people, and they decided to sabotage a ferry which would be carrying the heavy water across Lake Tinn on the Tinnsjø railway ferry. One of his recruits recognized a ferry-crew member and spoke with him, taking an opportunity to slip into the bottom of the ship, plant the bomb and slip away. Eight-and-a-half kilograms of plastic explosives (with two alarm-clock fuses) were fixed to the keel of the , which would transport railway cars with drums of the heavy water across Lake Tinn. The ferry and its cargo sank in deep water shortly after its departure around midnight on 20 February 1944. Witnesses reported seeing steel drums floating after the ferry sank, leading to