There have been a number of bottom-blows in the Navy, going back to at least 1981, which is the first I remember. Basically the Navy decides that they want to get rid of the bottom x% of poor performing Sailors.
Stars & Stripes reports:
More than 150 senior enlisted sailors are being separated after the Navy wrapped up its first continuation board last month, according to the Navy.
This appears to be 3% of those considered.