The Tainan's marking structure was complex. A separate 4-page appendix describes the markings in detail, including their final genesis when they transformed into the 251st kōkūtai. When the Tainan Naval Air Group was reorganized on 1 April 1942, the Dai-4 kōkūtai fighter component was already at Rabaul and Lae, and was absorbed into the Tainan. Given Japanese military efficiency the ‘V’ tail markings as directed by Japanese command appeared on the tails of the Tainan reisen shortly thereafter. At the time Dai-4 kōkūtai fighter component had a strength of two chūtai, but only sufficient reisen for one, the rest of its complement being Type 96 kansen. Dai-4 kōkūtai was then under the command of Lt Kawai Shirō, who had split off from the Tainan in 1941 to lead the Palau fighter detachment which was subsequently absorbed into Dai-4 kōkūtai. Until the Tainan’s main pilot cadre arrived in Rabaul on 16 April 1942 via Komaki Maru (the equivalent of two buntai of personnel), Kawai remained the Tainan's buntaichō.
By end of April 1942 there were about forty reisen in the Tainan. On paper, forty-five were allocated to the group, but they started losing some to combat before they reached their allocated strength. The initial breakdown by tail codes for the Type 21s was V-101 through V-115 (15 aircraft) for No. 1 chutai with red sash stripe; V-121 through V-135 (15 aircraft) with blue sash stripe for No. 2 chutai ; and V-150 though V-159 (10 aircraft) with yellow sash stripe for No. 3 chutai. The latter were former Dai-4 Kōkūtai aircraft and some did not receive Tainan Ku markings in time before going derelict at Lae, or being shot down.
Senior officers who arrived at Rabaul in April 1942 included hikōtaichō Lt-Cdr Nakajima Tadashi, and buntaichō Lt(jg) Sasai Jun’ichi. These two talented officers were joined in late April 1942 by two more buntaichō, Lt Yamashita Masao, and a month later Lt Yamashita Jōji. The latter brought with him a detachment of Chitose Kōkūtai pilots to reinforce the Tainan’s new potency, now fully staffed by four buntaichō and one hikōtaichō. The Chitose pilot reinforcements allowed the Tainan to mount several early missions at three chūtai strength - up to twenty-seven aircraft - for the first time.
Despite the attrition of New Guinea warfare throughout May/June/ July 1942, a group photo taken at Rabaul on 4 August 1942 exposes four buntaichō; Lt(jg) Sasai Jun’ichi, Lt Kawai Shirō, Lt Inano Kikuichi, and Lt Yamashita Jōji.
To further complicate matters, the Buna detachment, which operated mostly Type 32 reisen, adopted its own markings.