Hello all. Well, I know a bit about failure …
The preamble:
The wordplay in each clue leads to an extra letter in addition to those needed for the answer. Read in clue order these give 11 words describing the FAILURE of 13, a plan conceived by 15d. 1a was 1,6,3,3, which solvers must highlight. Chambers Dictionary (2016) is recommended.
No known failures to report filling the grid and collecting the wordplay letters:
TOO MANY THINGS COULD GO WRONG AND MOST OF THEM DID
The preamble and grid tell us these describe the failure of MARKET GARDEN, a plan conceived by MONTGOMERY. Operation Market Garden, an Allied military operation devised by Field Marshal Montgomery, ultimately failed in its objective to capture ARNHEM BRIDGE.
A quote regarding this operation, ascribed to Sir Frederick Browning in General Roy E. Urquhart’s memoir, has passed into idiom: I think we might be going
A BRIDGE TOO FAR
This we find in one of Chalicea’s favourite hiding places, diagonally in the grid. Thanks Chalicea!
If there is a setter’s blog for this puzzle it will be available after 9am here.

| # | ANSWER | Clue with definition underlined | |
| Explanation, with quoted indicators in italics and ANSWER letters in bold caps | |||
| Across | |||
| 11a | DUE | Appropriate composition for two performers (3) | T |
| DUE[T] (composition for two performers) | |||
| 12a | YOO-HOO | Boyhood mood exposed desperate cry for attention (6) | O |
| Without outer letters (… exposed) bOYHOOd mO[O]d anagrammed (desperate) | |||
| 14a | ULLING | Making good of leakage adapting globulin with no bulk primarily (6) | O |
| Anagramming (adapting) GL[O][b]ULIN with no B (Bulk primarily) | |||
| 15a | MORON | Somewhat feeble-minded person, member of Utah’s religious sect (5) | M |
| MOR[M]ON (member of Utah’s religious sect) | |||
| 17a | DIMS | Darkens transformation of Midas (4) | A |
| An anagram of (transformation of) MID[A]S | |||
| 18a | OVERT | No green colour evident (5) | N |
| [N]O + VERT (green colour) | |||
| 20a | IOTA | Tiny bit of a plaything I put back (4) | Y |
| A, TO[Y] (plaything) and I reversed (put back) | |||
| 21a | GRENADES | Good commodities for barter including base, finally malign weapons (8) | T |
| G (good) + [T]RADES (commodities for barter) including E (base) and finally maligN | |||
| 23a | TWISTIEST | Most convoluted bizarre tests with skill at heart involved (9) | H |
| An anagram of (bizarre) TESTS WIT[H], the middle letter of (… at heart) skIll included (involved) | |||
| 27a | ILLS | Misfortunes buried in civil list (4) | I |
| The answer is buried in civIL L[I]St | |||
| 29a | OMIT | Intentionally ignore input to Comintern (4) | N |
| Contained in (input to) cOMI[N]Tern | |||
| 31a | GRIEF | Sorrow of composer originally felt (5) | G |
| GRIE[G] (composer) + the first letter of (originally) Felt | |||
| 34a | NATURISM | Saturnism running wild, philosophy that requires habits to be discarded (8) | S |
| [S]ATURNISM anagrammed (running wild) | |||
| 35a | MOTOR | Second band of twisted metal in machine providing motive power (5) | C |
| MO (second) + TOR[C] (band of twisted metal) | |||
| 36a | WHAPS | Bumps occur in woods intermittently (5) | O |
| HAP (occur) in alternate letters of (… intermittently) Wo[O]dS | |||
| 37a | ELFS | Will’s tangles involved fuels (4) | U |
| An anagram of (involved) F[U]ELS | |||
| 38a | NAIL | Pin down North American misfortune (4) | L |
| N (North) + A (American) + IL[L] (misfortune) | |||
| 39a | ETEN | Giant bygone Bastille prisoner not socially acceptable (4) | D |
| [D]ÉTEN[u] (Bastille prisoner) not U (socially acceptable) | |||
| 40a | RIMAE | Depressing aged fissures (5) | G |
| [G]RIM (depressing) + AE. (aged) | |||
| 41a | HOLD SWAY OVER | Have power regarding showy overload in turmoil (12, three words) | O |
| SH[O]WY OVERLOAD anagrammed (in turmoil) | |||
| Down | |||
| 1d | AMMUNITIONING | Haplessly waiting on mum in provision of ways to fight (13) | W |
| An anagram of (haplessly) [W]AITING ON MUM IN | |||
| 2d | NIRLIT | Northern Ireland bishop literally pinched with cold in Aberdeen (6) | R |
| NI (Northern Ireland) + R[R] (bishop) + LIT. (literally) | |||
| 3d | EDEN | Old English hideaway paradise (4) | O |
| [O]E (Old English) + DEN (hideaway) | |||
| 4d | BEGUM | Commenced Mass for lady of high rank (5) | N |
| BEGU[N] (commenced) + M (mass) | |||
| 5d | RYALS | Young women locally embracing first and last of really old gold coins (5) | G |
| [G]ALS (young women locally) around (embracing) outer letters of (first and last of) ReallY | |||
| 6d | DODO | Fuss and celebration for character who is out of fashion (4) | A |
| [A]DO (fuss) and DO (celebration) | |||
| 7d | EON | No people turned up for a long time (3) | N |
| NO[N]E (no people) reversed (turned up) | |||
| 8d | POINTS OF ORDER | Open doors drift confusedly in formal queries concerning procedure (13, three words) | D |
| An anagram of (… confusedly) OPEN [D]OORS DRIFT | |||
| 9d | BALLOW | British Museum to admit Shakespeare’s cudgel (6) | M |
| B[M] (British Museum) + ALLOW (to admit) | |||
| 10d | AKITAS | It in Osaka funnily produces powerful dogs (6) | O |
| IT in an anagram of (… funnily) [O]SAKA | |||
| 16d | REDUIT | Dreadfully dustier inner fortified retreat (6) | S |
| An anagram of (dreadfully) DU[S]TIER | |||
| 17d | DETOUR | Regretted upset about retrograde excessive deviation (6) | T |
| RUED (regretted) reversed (upset) around (about) the reversal of (retrograde) OT[T] (excessive) | |||
| 19d | VAIR | Head of Armani coming in to see French fur (4) | O |
| The first letter of (head of) Armani coming in V[O]IR (to see, French) | |||
| 22d | REISSUE | Judge is occasionally astute in new release (7) | F |
| RE[F] (judge) + IS + occasionally aStUtE | |||
| 24d | ILLTH | Cultivate most of the opposite of wealth for Ruskin (5) | T |
| [T]ILL (cultivate) + most of THe | |||
| 25d | STAMINA | Endurance of sham involving time in America (7) | H |
| S[H]AM involving T (time) + IN + A (America) | |||
| 26d | SEROSAE | Watery membranes relax worriers now and then in retreat (7) | E |
| Backwards (… in retreat), EAS[E] (relax) plus alternate letters of (… now and then) wOrRiErS | |||
| 28d | SQUALL | Misgiving central to extremes of seasonal storm (6) | M |
| QUAL[M] (misgiving) is inside (central to) the outer letters of (extremes of) SeasonaL | |||
| 30d | MUISTS | Mud is origin of these singular disused Scottish powders (6) | D |
| MU[D] + IS + the first letter of (origin of) These + S (singular) | |||
| 32d | SAWAH | Noticed acre on outskirts of Hanoi is irrigated paddy-field (5) | I |
| SAW (noticed) + A (acre) + the exterior letters of (outskirts of) Hano[I] | |||
| 33d | FOLIO | Bend over on itself one old leaf (5) | D |
| FOL[D] (bend over on itself) + I (one) + O (old) | |||
I enjoyed the puzzle and found all the thematic material. I thought some of the clues were very hard and did not solve them all. Thanks Chalicea and Kitty.