What day of the week was June 11, 1865?

The day of the week June 11th, 1865 fell on was a Sunday.

The Naval Battle of Riachuelo is fought on the rivulet Riachuelo (Argentina) the between the Paraguayan Navy on one side and the Brazilian Navy on the other. The Brazilian victory was crucial for the later success of the Triple Alliance (Brazil, Uruguay and Argentina) in the Paraguayan War.