Danger warning, losing right old battle (5)
I believe the answer is:
alamo
'battle' is the definition.
(famous mission and siege from the Texas revolution)
'danger warning losing right old' is the wordplay.
'danger warning' becomes 'alarm' (I've seen this before).
'losing' suggests deleting specific letters.
'right' becomes 'r' (common abbreviation).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'alarm' with 'r' taken out is 'alam'.
'alam'+'o'='ALAMO'
(Other definitions for alamo that I've seen before include "historical Franciscan mission" , "The red planet" , "national monument" , "Mission building in Texas, site of famous siege by Mexico" , "Famous Texan mission" .)