The most common and most likely answer to this crossword clue is the 6 letter word LINERS
I've seen this crossword clue in The Daily Telegraph
L
I
N
E
R
S
More clues leading to the result LINERS
Buddy explains!

The straight part
We know that "Inner protections/ships" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case inner protections/ships = liners.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 LINERS mean?
LINERS noun- Someone who fits a lining to something.
- A removable cover or lining
- The pamphlet which is contained inside an album of music or movie
- A lining within the cylinder of a steam engine, in which the piston works and between which and the outer shell of the cylinder a space is left to form a steam jacket.
- A slab on which small pieces of marble, tile, etc., are fastened for grinding.
- Formal no show sock
- A large passenger-carrying ship, especially one on a regular route; an ocean liner.
- A ship of the line.
- A line drive.
- A basic salesperson.
- (in combination) Something with a specified number of lines.
- Short for penny-a-liner.