ACROSS
 9. ←EDIT EEL← = LEE TIDE <danger for small boats>
10. <superhero> AVENGER = GENEVA* R_
11. T_ OPS + E CRET[-e] = TOP-SECRET <classified>
12. <seize power from> USURP = US (R inside UP)
13. END inside KO = KENDO <martial art>
14. ←MO DRY TRAM← = MARTYRDOM <good reason for being late?>
16. (UNIONS + BRITAIN DO)* = INSUBORDINATION <open rebellion>
19. <choked> GARROTTED = GAR + ROTTED
21. <sword> SABRE = (.e)S A BRE(a.)
23. <military assault> SIEGE = ←IS← + EG E
24. <surrenders> ROLLS OVER = ROLL + SOVER_
26. TEA_ inside (MAN U) = MANTEAU <garment>
27. <warship> TRIREME = "TRY" + REME

DOWN
 1. <offensive> BLITZKRIEG = BILGE* outside (K inside RITZ)*
 2. <perhaps dirk> WEAPON = WON outside EA P
 3. D B outside (B-MOVIE)* = DIVE-BOMB <attack from the air>
 4. <equipment> GEAR = ←RA EG←
 5. STREAM* MIND = MASTERMIND <quiz show>
 6. <second-in-command> DEPUTY = DUTY outside EP
 7. <prayer> AGNUS DEI = ←(.l)IED SUNG A(n.)←
 8. ←PART← = TRAP <ambush>
14. MUM outside ORATORI[-o] = MORATORIUM <suspension>
15. <misunderstanding> MONDEGREEN = ON DEGREE inside MN
17. <police officer> SERGEANT = (GETS NEAR)*
18. <killer> ASSASSIN = IN after (ASS ASS)
20. YE D after OBE = OBEYED <followed command>
22. BOER outside VV = BOVVER <gang violence>
23. <wrestling> SUMO = SO outside UM
25. LA[-s]TS = LATS <muscles>