on - Am ur . ▁ ▁The ▁standard ▁aircraft ▁crew ▁consisted ▁of ▁the ▁pilot , ▁gun ner ▁and ▁observer ▁and ▁the ▁aircraft ▁was ▁able ▁to ▁carry ▁ ▁of ▁bomb s ▁for ▁up ▁to ▁. ▁Some ▁were ▁built ▁with ▁flo ats ▁as ▁the ▁MP - 6 , ▁( also ▁known ▁as ▁K R - 6 P ), ▁for ▁mar itime ▁pat rol ▁duties . ▁Another ▁variant ▁was ▁the ▁K R - 6 ▁( K R ▁– ▁Kre iser ▁Raz vey ed ch ik ▁– ▁cru iser ▁reconna issance ), ▁which ▁had ▁two ▁P V - 2 ▁machine ▁guns ▁and ▁a ▁second ▁gun ner , ▁later ▁re leg ated ▁to ▁training ▁duties . ▁ ▁By ▁ 1 9 3 5 , ▁the ▁R - 6 ▁was ▁becoming ▁ob sole te , ▁and ▁several ▁were ▁transferred ▁to ▁Aer of lot ▁and ▁A via ▁Ar kt ika , ▁which ▁used ▁them ▁to ▁carry ▁passengers ▁and ▁cargo ▁in ▁Si ber ia ▁before ▁the ▁Great ▁Patri otic ▁War , ▁designated ▁PS - 7 - 2 M 1 7 ▁( the ▁" 2 M 1 7 " ▁showed ▁that ▁the ▁aircraft ▁were ▁power ed ▁by ▁two ▁Mik ul in ▁M - 1 7 s ), ▁or ▁as ▁MP - 6 - 2 M 1 7 ▁if ▁ ▁flo ats ▁were ▁attached . ▁ ▁Vari ants ▁Data ▁from : ▁The ▁O sp rey ▁Encyclopedia ▁of ▁Russian ▁A ircraft ▁ 1 8 7 5 – 1 9 9 5 ▁AN T - 7 The ▁OK B ▁design ation ▁of ▁the ▁project ▁and