It was a Thursday.
It can be on any day of the week. It will depend on the year. As this question was asked in March 2013, then the 7th of April in 2013 was on a Sunday.
7 March 1985 was a Thursday.
March 7 1972 was a Tuesday.
March 7, 1945 was a Wednesday.
March 7 2011 will be a Monday.
March 7, 1979 was a Wednesday.
March 7, 1995 was a Tuesday.
March 7 1950 was a Tuesday.
March 7, 1983 was a Monday.
March 7 2010 was a Sunday.
March 7, 1961 was a Tuesday.
March 7, 1946 was a Thursday.