Tree specially hollowed out happened to hide soldiers (8)
I believe the answer is:
sycamore
'tree' is the definition.
(I know that Sycamore is a type of tree)
'specially hollowed out happened to hide soldiers' is the wordplay.
'hollowed out' says to hollow out the word (remove centre letters).
'happened' becomes 'came' (to happen upon and to come upon mean to encounter).
'to hide' means one lot of letters goes inside another.
'soldiers' becomes 'OR' (Other Ranks).
'specially' with its centre taken out is 'sy'.
'came' placed around 'or' is 'camore'.
'sy'+'camore'='SYCAMORE'
(Other definitions for sycamore that I've seen before include "Tree for the odd Rose Macy" , "Great maple tree" , "Tree with two-winged fruit" , "Deciduous tree" , "Species of maple" .)