Renewed fighting between the French and the insurgents (in the guise of the 308th and 312th Divisions, commanded by Võ Nguyên Giáp) broke out in January 1951 at Vĩnh Yên, located in the Tonkin region. Air cover for the French army's "mobile groups" led by de Lattre was provided by two fighter groups, namely III/6 ""Roussillon"" and I/9 ""Limousin"", which were able to muster about forty P-63s, and these were reinforced by eight F6Fs lent from II/6 "Normandie Niemen" and I/6 ""Corse"." During the month, more than 1,700 fighter sorties were flown by 114 out of the 147 aircraft, mostly from Gatac North, then in service protecting Hanoi, while the ""Normandie-Niemen"" fighter group was charged with the protection of the southern sector. French bombing capability was very much enhanced with the operational missions flown by dedicated B-26 bombers, assigned to GB I/19 ""Gascogne"", during the battle for Mao-Khe (which was the center of the coal mine region in northern Vietnam, and its loss would hurt the French) to protect Haiphong. Giap himself was partly to blame for the fact that the Việt Minh had been trounced, since air power, which had seen Vĩnh Yên remain in French hands, and naval power, which had seen Mạo Khê remain in French hands, were beyond his experience, and he had thus not planned for them.