What was the bloodiest year in Vietnam?

The Tet Offensive began the bloodiest period and it started at the end of 1967. So, the highest casualites may be for 1968. BTW, the Viet Nam War Memorial Wall in Washington DC, has names of those killed in the war arranged in chronoligical order of the date of their death. The highest point in the wall is therefore at the period of 1967/68.