The most common and most likely answer to this crossword clue is the 7 letter word SAPPERS
S
A
P
P
E
R
S
Buddy explains!

The straight part
We know that "E/R/E" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case e/r/e = sappers.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SAPPERS mean?
SAPPERS noun- One who saps; specifically, one who is employed in working at saps, building and repairing fortifications, and the like. Often known as a combat engineer or military engineer.
- An officer or private of the Royal Engineers.