The most common and most likely answer to this crossword clue is the 7 letter word MARINES
I've seen this crossword clue in The Daily Telegraph
M
A
R
I
N
E
S
More clues leading to the result MARINES
- Resistance infiltrating state’s elite corps
- More than one jolly complicated seminar
- More than one serviceman remains unreliable
- US state’s protecting Republican force
- Uniformed people from another planet, interning in earth
- Sailors' remains at sea
- Branch of the armed services remains in need of reform
- Horses carrying in soldiers
- Horses carrying in armed forces
Buddy explains!

The straight part
We know that "force" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case force = marines.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 MARINES mean?
MARINES noun- A soldier, normally a member of a marine corps, trained to serve on board or from a ship
- Capitalised in the plural A marine corps.
- A painting representing some marine subject.
- A military organization of marines, soldiers who are trained and equipped to fight on or from ships.