Weapon's power deployed by Eisenhower (4)
I believe the answer is:
pike
'weapon's' is the definition.
(pike is a kind of weapon)
'power deployed by eisenhower' is the wordplay.
'power' becomes 'p' (symbol in physics).
'deployed by' means one lot of letters go next to another.
'eisenhower' becomes 'Ike' (Ike was a nickname of President Dwight Eisenhower).
'p'+'ike'='PIKE'
(Other definitions for pike that I've seen before include "Old weapon -- Dad's Army character" , "Fish - medieval weapon" , "Voracious freshwater fish" , "Fish and pole with a spearhead" , "Former infantry weapon" .)