Under Krell's command, Appo stood by the Jedi General on the top of a cliff, while the other clone squads, led by Clone Captain CT-7567—nicknamed "Rex"—engaged the Umbarans in combat. After receiving the order of forming clone trooper platoons from Krell, Appo obeyed the order and organized a number of clone platoons that consisted of clone troopers and AT-RT-mounted troops. As Rex and his men were taking causalities while battling six-legged Umbaran mobile heavy cannons, Appo informed Krell that his task of forming the platoons was complete. The Clone Sergeant also wanted to send the troops to aid Rex on the battlefield, although Krell dismissed Appo, by stating he would give out the order of deploying the soldiers. When Rex contacted Krell via hologram, Appo held the hologram's transmitt