Hanuman destroyed the entire Ashokvana ,the news reached Ravana ,he grew angry and sent a large army ordering to get the "kapi".Hanuman's valorous deed arouse lot of devotion admiration among satvik souls ,but Ravan despite having ten heads and having listened to this deed with twenty ears could only hate him more.
Ravana sent 80crore excellent senapatis (not just soldiers),lead by 80000 excellent warriors. These were armed with all types of weapon ,above that were protected by the boon of Rudra ,of being immortal.They simultaneously attacked Hanuman with all force and weapons.sending this much force on a single monkey establishes the fact as how much aggrieved Ravana was by the news of destruction of ashokvatika.
Despite this big force attacking simultaneously ,it appeared as a hit of garland thrown on a intoxicated elephant,to Hanuman.Siva is layakaraka, his devotees Rakshasas all too got "laya" by the Vayuputra ,who is also the regulator of Shiva.He killed all the 80crore 80000 army within minutes.
He also killed seven sons of Ravana's ministers ,they were all huge like mountains in dimensions. Ravana then sent almost 1/3rd of his army lead by virupaksha,yupaksha,dhurdhara,praghas and bhaskarna ,these were all protected by boons from Bramha and Rudra and entered battlefield garden with complete overconfidence .These alongwith entire 1/3rd army were killed by Hanuman. Hanuman could have killed entire Ravana's army that very day itself, but he stopped the destruction with 1/3rd only .
[This way Hanuman single handedly defeated Ravana's army within no time giving jitters to Ravana and other demons that if one monkey could bring such disaster then what if Rama with his other monkey's attack.]