The new Ki-61 "Hien" fighters entered service with a special training unit, the 23rd "Chutai", and entered combat for the first time in early 1943, during the New Guinea campaign. The first "Sentai" (Air Group/Wing) fully equipped with the "Hien" was the 68th in Wewak, New Guinea, followed by the 78th "Sentai" stationed at Rabaul. Both units were sent into a difficult theatre where jungles and adverse weather conditions, coupled with a lack of spares, quickly undermined the efficiency of both men and machines. Because the Ki-61 was so new, and had been rushed into service, it inevitably suffered from teething problems. Almost all of the modern Japanese aircraft engines, especially the Ki-61's liquid-cooled engines, suffered a disastrous series of failures and ongoing problems, which resulted in the obsolescent Ki-43 still forming the bulk of the JAAF's fighter capability.