Across:
   1. Savage extremes of bomber unit appal (6)
   5. A cigar smoked during May 8 celebration where the Reverend lives (8)
   9. see 4 down or 5 down
  10. Some alcohol consumed, initially under cover, can be for Tampa Bay team (10)
:  11. Mad rort: my foolish death for the cause (9)
  12. Bedding for animal with skin problems returning (5)
  14. Child tracks soldiers (8)
  16. Ranks of Mars' army on the move, with thousands lost (6)
  17. see 21
  19. Biden so upset, holding nothing for inconsequential folks (8)
  21,17. Who would want to repeat this tragedy regularly? Who, truly down at rite, who? (5 3 3)
  22. Half of Russia turned to deliver yield (9)
  25. Length and breadth of sin son contrived, chasing a bit of coin? (10)
  26. Peaceful pursuit of dozens (3)
  27. Company enjoyed breaking cover with May change (8)
  28. Theologian essentially pans Elmo (6)
Down:
   2. As borders may be, when war derogates returning bounds (7)
   3. Attempt street get-together (5)
   4. Celebrated May 8 with drink without hesitation (10)
   5,9ac. Even I'd party (coy I)... our wild celebration after 21 17! (7 2 6 3)
   6. Company leader put down inert pigeon (4)
   7. Strange trend - with so much repetition - came back in (9)
   8. Country regiment briefly turned back by many (7)
  13. Operation of 23 attacking USSR, as so revolutionary in pursuit of a couple of measures (10)
  15. Sickness in aorta perhaps, which has killed too many people (9)
  18. Someone given black badge by 23 in America, so CIA locatable (7)
  20. Europe learnt chaos could be ongoing (7)
  23. They erased half of European Jews! (5)
  24. AI's a revolutionary and big part of our world (4)
Solution:
BRUTAL=VICARAGE|
=E=R=I=I=L=E=E=|
=DAY=BUCCANEERS|
=R=S=E=T=Y=N=M=|
MARTYRDOM=STRAW|
=W===A=R=B=E=N=|
INFANTRY=ARRAYS|
===R=I=I=R=E===|
WARTWO=NOBODIES|
=S=I=N=E=A===T=|
WORLD=SURRENDER|
=C=L=A=R=O=A=R=|
DIMENSIONS=ZEN=|
=A=R=I=P=S=I=A=|
PLAYMATE=ANSELM|
Name: Puzzle 849 - Wild Party
Author: by BenDR