The most common and most likely answer to this crossword clue is the 6 letter word HUSSAR
H
U
S
S
A
R
More clues leading to the result HUSSAR
- Soldier and reformer meeting a king
- Cavalryman unwise to hold Soviet Union's leaders back
- Horseman spots revolutionary engaging our lot
- Soldier from America infiltrating Soviet Union to the east of Hungary
- Soldier, one in the main near a Queen
- Soldier mounted stairs, skipping every other one, in pursuit of swimmer
- Fish, carp skinned for old cavalryman
- Cavalryman‘s shout of joy heard
- In irritation, say, 4 x 4 almost knocked over horseman
- Horse approaching former Soviet territory carrying a
Buddy explains!

The straight part
We know that "I had mounted battles" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case i had mounted battles = hussar.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 HUSSAR mean?
HUSSAR noun- A member of the national cavalry of Hungary, Croatia and Poland.
- A member of the light cavalry of any of several European armies.