The 74th transitioned to P-51C-7 Mustangs in August, and on September 3 Herbst shot down two Japanese aircraft that he reported as Aichi D3A "Val" dive bombers but were probably Mitsubishi Ki-51 "Sonia" models instead. These were the first P-51 victories of the 74th FS. By September 16, Herbst's USAAF tally reached nine victories, five in a Mustang. Herbst appreciated the ability of the P-40 to absorb damage in low-level combat such as close support of infantry. For finer work such as dogfighting, dive bombing and skip bombing, he said, "I'll take the P-51 every time". Raised to the rank of major in July 1944, Herbst was given free rein in his command of the 74th Squadron. Using the radio call sign "Guerrilla", his squadron fought against Japanese forces conducting Operation Ichi-Go, a successful drive to consolidate communications along rail lines. In his first three months of combat, Herbst completed the required 100 combat sorties and was from that time forward officially restricted to administrative flights. However, Herbst's idea of "administrative" flights was very broad and aggressive, including weather assessment and new pilot training in areas where Japanese aircraft were known to be operating. He flew as an "observer" on combat missions in which he scored against enemy aircraft. Ten or eleven of Herbst's aerial victories were achieved during "administrative" flights. On one such flight on September 5, 1944, Herbst was ferrying his Mustang fighter to a more sophisticated airfield in Liuliang, China, because the ejector chutes of three of its six machine guns were not working properly and needed expert attention. Herbst encountered two groups of enemy fighters, one group at and another group at a lower altitude. Alone against the hostile force and with only half of his guns working, Herbst made a head-on attack against the top group, killing the leader. His aircraft was hit repeatedly by enemy rounds, shattering the canopy. More enemy aircraft joined the whirling battle against Herbst. With blood from deep scalp cuts partially blinding him, Herbst continued dogfighting, damaging other fighters and probably killing another flight leader. Finally, his last gun stopped working and he dived away to land safely at Kanchow Airfield. The performance earned him a Purple Heart and a Silver Star. Most accounts of this action describe Herbst fighting 32 aircraft total—16 high and 16 low—but Luther "Luke" Kissick, the intelligence officer of Herbst's squadron, writes that there were two flights of 8 at 10,000 ft protecting an unknown number below.