One attacks occasionally dumb loyalty (1-4)

I believe the answer is:

u-boat

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'one attacks occasionally dumb loyalty' is the definition.
I can't tell whether this defines the answer.

'occasionally dumb loyalty' is the wordplay.
'occasionally' indicates alternate letters (letters taken at regular intervals or occasions).
'dumb'+'loyalty'='dumbloyalty'
The alternate letters of 'dumbloyalty' are 'U-BOAT'.

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(Other definitions for u-boat that I've seen before include "Sea vessel" , "German wartime submarine" , "About (anag)" , "Submersible warship armed with torpedoes" , "Submersible warship of WWII" .)

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