| 101st Division Unit | Callsign | Helmet Decal | In Dutch |
| The 101st Airborne Division | Kangaroo | — | — |
| Divisional Headquarters / HQ-Company | Klaxon | Square (tick at 12) | Vierkant |
| 501st Parachute Infantry Division | Klondike | Diamond | Ruit |
| 502nd Parachute Infantry Regiment | Kickoff | Heart | Hart |
| 506th Parachute Infantry Regiment | Kidnap | Spade | Schoppen |
| 327th Glider Infantry Regiment | Keepsake | Clover | Klaver |
| 326th Engineers | Kiwi | E | E |
| 81st Anti Aircraft | Kentucky | Triangle | Driehoek |
| Division Artillery (Divarty) | Kingfish | Circle (tick at 12) | Cirkel |
| 321st Glider Field Artillery Battalion | Kansas | Circle (tick at 3) | Cirkel |
| 377th Parachute Field Artillery Battalion | Kite | Circle (tick at 6) | Cirkel |
| 463rd Parachute Field Artillery Battalion | Keynote | Circle (2 ticks 6) | Cirkel |
| 907th Glider Field Artillery Battalion | Kilogram | Circle (tick at 9) | Cirkel |
| 326th Medical Company | Kindergarten | Cross | Kruis |
| 426th Quartermaster Company (QMC) | Kitchen | Square (tick at 6) | Vierkant |
| 801st Ordnance Company | Kildare | Square (tick at 9) | Vierkant |
| Division Signal Company | Kilowatt | Square (tick at 3) | Vierkant |
| Division Recce (Recon) Platoon | King | Square (tick at 12) | Vierkant |
| 101st Military Police (MP) Platoon | — | MP | MP |
Infantry Regiments use additional ‘ticks’ to helmet decal at 12-3-6-9 o’clock position.
| 12 O’clock Tick | indicates | HQ & HQ Company | |
| 3 O’clock Tick | indicates | 1st Battalion (RED) | (Able – Baker – Charlie Company) |
| 6 O’clock Tick | indicates | 2nd Battalion (WHITE) | (Dog – Easy – Fox Company) |
| 9 O’clock Tick | indicates | 3rd Battalion (BLUE) | (George – Hotel – Item Company) |
Operations 101st Airborne Division prior to Market Garden:
| Operation Eagle | Dress Rehearsal for D-Day (UK) | 9th to 12th May 1944 | |
| Operation Neptune | Assault phase of Allied Invasion of Normandy | 5th / 6th June 1944 (D-Day) | |
| Initial verbal challenge for | D-Day: | Flash | |
| Password: | Thunder | ||
| Answer: | Welcome | ||
These Challenges & Passwords changed periodically (as shown in the D-Day (Overlord) table below).
| Challenge | Reply | ||
| H Hour | to 23.59 hrs D-Day | FLASH | THUNDER |
| 00.00 hrs D +1 | to 23.59 hrs D + 3 | THIRSTY | VICTORY |
| 00.00 hrs D + 4 | to 23.59 hrs D + 6 | WEAPON | THROAT |
| 00.00 hrs D + 7 | to 23.59 hrs D + 9 | WOOL | RABBIT |
* Unclear if the Reply was followed with an Answer like with the initial Flash-Thunder-Welcome.
No veteran could tell me what happened if a password was given of ‘a day before’. It is likely to asume that would have been accepted.
Challenges & replies during Market Garden
Top Secret APO 472, U.S. Army
Dated 15 September 1944
No. Of Copies: 150
HQ 101st Airborne Division
Office of the AcofS, G-2
Subject: Counter-Signs.
To: Unit Commanders
The following challenges and replies will be used in this operation on the dates indicated;
| Challenge | Reply | ||
| H Hour | to 23.59 hrs D-Day | RED | BERET |
| 2359 hrs D-Day | to 2359 hrs D + 1 | UNCLE | SAM |
| 2359 hrs D + 1 | to 2359 hrs D + 2 | CARRIER | PIGEON |
| 2359 hrs D + 2 | to 2359 hrs D + 3 | AIR | BORNE |
| 2359 hrs D + 3 | to 2359 hrs D + 4 | ROBERT | BURNS |
| 2359 hrs D + 4 | to 2359 hrs D + 5 | TROOP | CARRIER |
In the case of British SAS troops, the word NANCY will be used.
Use of the word NANCY identifies person as SAS personnel.
These challenges and replies will be memorized and this memorandum destroyed prior to leaving the U.K.
Under no circumstances will the challenges and replies be carried into the Operation in written form.
Sources: National Archives – Epic of the 101st Airborne Division
Screaming Ducks – D.C. van den Bogert