A secret American military unit known for its deception and trickery during World War II was awarded the highest honor, a Congressional Gold Medal, on Thursday in Washington, D.C.

The 23rd Headquarters Special Troops, also known as the "Ghost Army," used things like inflatable tanks, sound effects, costumes and acting to accomplish their missions in Europe.

“The actions of the Ghost Army helped change the course of the war for thousands of American and Allied troops and contributed to the liberation of a continent from a terrible evil,” Secretary of the Army Christine Wormuth said during the ceremony at the U.S. Capitol, the Associated Press reported.

Only seven members of the Ghost Army are still alive, the AP reported, and three attended the ceremony in Washington: 100-year-old Bernard Bluestein of Hoffman Estates, Illinois; 99-year-old John Christman of Leesburg, New Jersey; and 100-year-old Seymour Nussenbaum of Monroe Township, New Jersey.

What was the Ghost Army?

After the war, information on the Ghost Army was kept secret for more than 50 years until it was declassified in 1996.

The military unit consisted of around 1,000 men and 82 officers under Colonel Harry L. Reeder.

Despite their relatively small numbers, the Ghost Army was able to simulate around 30,000 men, or two divisions, by using radio, sonic and visual deception, according to the National World War II Museum.

What is the Congressional Gold Medal?

The Congressional Gold Medal is the oldest award and the highest civilian honor given in the U.S., along with the Presidential Medal of Freedom.

It is awarded by Congress and is the "highest expression of national appreciation for distinguished achievements and contributions by individuals, institutions or groups," according to the Congressional Medal of Honor Society's website.