It was a Tuesday
18th December 1957 was a Wednesday.
December 18th, 1918 fell on a Wednesday.
December 18th, 2007 fell on a Tuesday.
December 18th, 1947 fell on a Thursday.
December 18th, 1956 fell on a Tuesday.
December 18th, 1991 fell on a Wednesday.
Tuesday
The question was asked on the 18th of December 2011. In 1994 the 18th of December was on a Sunday.
Monday
December 18th
December 18th 1968 was a Wednesday.
December 18, 1969 was a Thursday.