[2][3] Portugal officially recognized the United States with the acceptance of U.S. Minister David Humphreys' credentials on May 13, 1791.

[2] The U.S. legation in Lisbon became an embassy on June 20, 1944, elevating the diplomatic representation to the ambassadorial level with Raymond Henry Norweb presenting his credentials as Ambassador.

It was committed by Marxist terrorists belonging to the Popular Forces 25 April (PF-25) group, calling the embassy an American imperialist threat to Portuguese independence.

[4] The next month, four mortar shells were fired by the group at the compound, again only causing damage to cars.

The bomb was discovered by the Portuguese guards and managed to run away [dubious – discuss] just before it detonated and destroyed the vehicle.