D - 4 1 : ▁A ▁U DM H / N 2 O 4 ▁burning ▁engine ▁in ▁the ▁gas ▁generator ▁cycle . ▁Development ▁years : ▁ 1 9 7 3 - 1 9 7 5 ▁. ▁For ▁use ▁on ▁the ▁second ▁stage ▁of ▁R - 2 9 R . ▁Sub mer ged ▁in ▁the ▁prop ell ant ▁tank . ▁ 3 D - 4 2 : ▁A ▁U DM H / N 2 O 4 ▁burning ▁engine ▁in ▁the ▁gas ▁generator ▁cycle . ▁Development ▁years : ▁ 1 9 7 3 - 1 9 7 5 ▁. ▁For ▁use ▁on ▁war head ▁of ▁the ▁ ▁R - 2 9 R ▁. ▁Four ▁fixed ▁main ▁comb ust ion ▁ch amb ers ▁and ▁four ▁vern iers . ▁ 3 D - 6 7 ?: ▁A ▁U DM H / N 2 O 4 ▁burning ▁engine ▁in ▁the ▁gas ▁generator ▁cycle . ▁Development ▁years : ▁ 1 9 7 6 - 1 9 8 0 ▁. ▁For ▁use ▁on ▁war head ▁of ▁the ▁R - 3 9 . ▁D ual - mode ▁ro cket ▁engine ▁with ▁multiple ▁reg imen . ▁ 3 D - 3 6 : ▁A ▁U DM H / N 2 O 4 ▁burning ▁engine ▁in ▁the ▁gas ▁generator ▁cycle . ▁Development ▁years : ▁ 1 9 8 0 - 1 9 8 6 ▁. ▁For ▁use ▁on ▁war head ▁of ▁the ▁R - 2 9 R M . ▁Z D - 3 8 : ▁A ▁U DM H / N 2 O