Operation Una
Order of battle

Corps
Unit
Notes
Zagreb
1st Guards Brigade
In the area of Dvor
Zagreb
2nd Guards Brigade
In the area of Hrvatska Dubica
Zagreb
17th Home Guard Regiment
In the area of Hrvatska Dubica
Zagreb
General Staff Reconnaissance Sabotage Company
In Hrvatska Kostajnica
Bjelovar
52nd Home Guard Regiment
In Jasenovac area, a battlegroup of 770 troops
Bjelovar
121st Home Guard Regiment
In Jasenovac area, a battlegroup of 911 troops
Bjelovar
125th Home Guard Regiment
In Jasenovac area, a battlegroup of 800 troops
Bjelovar
16th Artillery-Rocket Brigade
One battalion of 155-millimetre (6.1 in) howitzers only, 237 troops
Bjelovar
18th Artillery Battalion
A platoon of 155-millimetre howitzers and a platoon of 130-millimetre (5.1 in) gun, 106 troops
Bjelovar
34th Engineer Battalion
Also utilising equipment of the 33rd Engineer Battalion
Bjelovar
69th Military Police Company
-

Question: Who  sent the 121st Home Guard Regiment battlegroup to Jasenovac, as reinforcement?
Answer: The Bjelovar Corps sent the 121st Home Guard Regiment battlegroup to Jasenovac, as reinforcement.