What is 'e. m.' in this sentence?

The expression “e.m.” is short for “enlisted men”.

To go by the other terms in the quoted passage, this is an American writing about an American military operation.

The contemporary rank structure in the U.S. Army can be found here: https://www.army.mil/ranks/

The term “enlisted men” has been superseded by “enlisted soldiers”.

Most people are familiar with the broad difference between a commissioned oficer and an enlisted soldier. There is, however, the intermediate rank of warrant officer, which has a long history of its own: https://en.m.wikipedia.org/wiki/Warrant_officer

The different branches of the U.S. military make use of the warrant officer rank in different ways. Some warrant officers are equivalent to commissioned officers, but most of the WO ranks are seen as enlisted soldiers.

Given that the text mentions only officers and enlisted men, there were either no warrant officers present, or they were counted as either officers (possible) or as enlisted men (most likely).

A senior warrant officer is often a highly trained specialist (e.g. an Army helicopter pilot). In a military report identifying the “significance” of the soldiers being evacuated, it would make sense to identify them.