The nuclear capable MiG-21s were equipped with a special control box fixed under the upper part of the windscreen. That device allowed
the pilot to choose between conventional weapons or a tactical nuclear bomb and it included all the controls related to the special weapon.
Also, additional fuses related to that control box were located inside the cockpit.
Thanks to that device, an aircraft wired to carry a tactical nuclear bomb could therefore either fly a combat mission armed with usual conventional weapons
(unguided rockets, air-to-air missiles,
bombs) or fly a special combat mission armed with a single nuclear bomb.
Also, MiG-21SM were equipped with a special control box located at the same place. However, this switchbox was used to control a SPS-141 ECM pod and ASO-2I flare
launchers. MiG-21R reconnaissance aircraft also were equipped with different control box variants depending on the reconnaissance pod model that the aircraft
was carrying. Although externally somewhat similar, those various control boxes are not to be confused with those dedicated to special weapons.
MiG-21PFM (94N) control box
1. "Protection" - Status light on: security device for the nuclear bomb to prevent
any accidental detonation before dropping
2. "Suspended" - Status light on: nuclear bomb attached
3. "Explosion" - Status light on: nuclear bomb armed
4. "Combat drop"
5. Activation of the special weapon's fuse for either an "air" (switch up) or a "ground" burst (switch down)
6. "Brake" - activation of the nuclear bomb braking parachute
7. Selection knob: "unguided rockets"
8. Selection knob: "K-5 missiles" (K-5M = RS-2U / AA-1A "Alkali")
9. Selection knob: "bombs" (conventional)
10. Selection knob: "special aviation bomb"
11. "Emergency drop" of the nuclear bomb (chronology: switch n°12, then switch n°11)
12. Selection switch up: "Emergency drop with detonation" / Switch down: "no detonation"
MiG-21bis / MiG-21SMT control box
1. "Suspended" - Status light on: nuclear bomb attached
2. "Explosion" - Status light on: nuclear bomb armed
3. "Protection" - Status light on: security device for the nuclear bomb to prevent any accidental detonation before dropping
4. "Emergency drop" of the nuclear bomb (chronology: switch n°5, then switch n°4)
5. Selection switch up: "Emergency drop with detonation" / Switch down: "no detonation"
6. "Combat drop"
7. Selection switch up: "special aviation bomb" / Switch down: "unguided rockets, missiles, bombs, cannon"
8. "Brake" - activation of the nuclear bomb braking parachute
9. Activation of the special weapon's fuse for either an "air" (switch up) or a "ground" burst (switch down)
