Rough sketches outlining germ warfare devices of 1940s (10)

I believe the answer is:

doodlebugs

'warfare devices of 1940s' is the definition.
(German bombs in World War Two)

'rough sketches outlining germ' is the wordplay.
'rough sketches' becomes 'doodles' (I've seen this before).
'outlining' is an insertion indicator (some letters create an outline round others).
'germ' becomes 'bug' (synonyms).
'doodles' placed around 'bug' is 'DOODLEBUGS'.

I've seen this clue in The Guardian.

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