NRP Augusto de Castilho was a warship in service of the Portuguese Navy during World War I.

It was sunk in combat while escorting the steamer São Miguel,[1] originating the last Portuguese casualties of that conflict.

The Portuguese patrol ship opened fire at about 500 metres (1,600 ft) at the unidentified submarine, which dived promptly.

On 13 October while escorting the passenger ship São Miguel, Augusto de Castilho, under the command of First Lieutenant Carvalho Araújo, sighted by the German submarine SM U-139.

The Portuguese warship was sunk after a fierce two-hour battle with the loss of four crewmembers, among them Carvalho Araújo.