Secret soldiers behind hotel window (4)

I believe the answer is:

sash

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'window' is the definition.
(I've seen this before)

'secret soldiers behind hotel' is the wordplay.
'secret soldiers' becomes 'sas' (Special Air Service. I am not sure about the 'secret' bit.).
'behind' says to put letters next to each other.
'hotel' becomes 'h' (phonetic alphabet: alpha, bravo, charlie etc.).
'sas'+'h'='SASH'

Can you help me to learn more?

(Other definitions for sash that I've seen before include "Decoration for the twelfth" , "Broad band, the one me father wore?" , "Girdle" , "Window frame; silk band" , "Popular band in Northern Ireland" .)

I've seen this clue in The Sun.

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