'Washing' was a British operation by the Special Operations Executive to destroy the Asopos railway viaduct in the area of central Greece to the north-west of Athens (20 June 1943).

After the German invasion of Greece in 1941, British military missions in the Balkans were instructed to make a maximum effort to sabotage the German and Italian war effort, with the Axis lines of communication a primary target. The Asopos viaduct on the railway line connecting Thessaloníki and Athens, some 12 miles (19.25 km) to the south of Lamia, was strongly guarded and especially difficult to approach, but its destruction would cut all rail communication between the north and south of Greece for at least two months.

The viaduct crossed the Asopos river, which rises out of a glacier on Mt Giona, and falls through several thousands of feet over several cascades before reaching the valley bottom, running east for several miles and then falling into a deep gorge. This ducts the fast-flowing river along about 1.5 miles (2.4 km) of waterfalls, sluices and whirlpools before dropping another 1,000 ft (305 m) and finally debouching out of the mountains onto the plain.

At the highest and narrowest point of the gorge, the railway line emerged from a tunnel and crosses a long steel viaduct, before re-entering the tunnel on the other side. From the centre of the main span to the river bed was a drop of about 200 ft (60 m). Round the mouth of the tunnel on the northern side were the huts accommodating the German guard of some 50 men, as well as searchlight and machine gun positions. The approaches to this area were heavily wired and mined.

In May, following a report that the guard detachment on the viaduct was being strengthened and the base of the structure reinforced, the British Middle East headquarters in Cairo decided that the viaduct had to be destroyed without further delay. Captain Geoffrey Gordon-Creed was chosen to establish a military mission in the Greek provinces of Dorice and Parnassos, and in March 1943 he was parachuted into the area of Mt Giona. After a careful reconnaissance, in which Lieutenant Stott, a New Zealander, played a leading role, the decision was made that the only possibility was to move down the seemingly impassable gorge at night from a direction which would be least expected, scale the 200-ft (60-m) cliffs up to the abutments, climb on to the main structure, and finally set the charges before escaping back up the gorge.

On the night of 31 May, an attacking party of three officers and two non-commissioned officers under the command of Gordon-Creed set off. After marching through the night, with four mules to help carry their stores and explosives, they camped at the head of the gorge at first light. Every morning, for the next 18 days, the men crawled out of their blankets, brewed up something hot and entered the icy river. They took it in turns to swim ahead with the rope, relayed by the others until it was possible to clamber on to a rock farther downstream and make fast for the others to follow. Hours of swimming, struggling and climbing, where any slip would have meant almost certain death by drowning or being swept over a waterfall, allowed them to move only a few yards farther down the gorge.

On the morning of 18 June, the men of the party sighted their target. The bridge, abutments and spans were covered with scaffolding which, they hoped, would make their task easier. They laid up for two days, and by 20.00 on 20 June were in the river under the bridge carrying their explosives but, to facilitate the climb ahead, armed only with coshes. Gordon-Creed and Stott led, and would have been in full view of the guards if the searchlights been directed downward. They had just reached the girders of the bridge when, glancing upwards, Gordon-Creed saw a sentry only a short distance above him. When the sentry went off duty, he decided to take a stroll in the moonlight before turning in. With discovery imminent, Gordon-Creed coshed the man and tipped him into the depths of the gorge. After setting the charges with two-hour fuses, the attacking party’s men were three-quarters of the way home, and up to their necks in a deep pool, when they heard a huge roar. The viaduct fell into the gorge, and its complete destruction was confirmed by air reconnaissance photographs shortly after this. The men returned to base exhausted, with the skin on their arms and legs in ribbons.

Sure that the destruction of the viaduct could have been the result only of treachery, the Germans executed the guard commander and 10 of his men.