▁was ▁multip lied ▁by ▁ 2 6 ▁compared ▁with ▁a ) ▁and ▁b ), ▁but ▁the ▁introduction ▁of ▁a ▁fourth ▁wheel ; ▁it ▁was ▁not , ▁it ▁is ▁true , ▁intended ▁primarily ▁for ▁this ▁purpose ▁but ▁was ▁added ▁to ▁carry ▁out ▁inter change able ▁working ▁with ▁the ▁Naval ▁En igma . ▁ ▁History ▁of ▁Ger ät ▁ 3 9 ▁Model ▁a ) ▁had ▁been ▁developed ▁as ▁early ▁as ▁the ▁year ▁ 1 9 3 9 ▁or ▁ 1 9 4 0 ▁at ▁Wa ▁Pr ue f ▁ 7 ▁at ▁the ▁W affen amt . ▁In ▁the ▁summer ▁of ▁ 1 9 4 2 , ▁a ▁prototype ▁was ▁available ▁at ▁Dr . ▁Pu pp ' s ▁labor atory ▁at ▁Wa ▁Pr ue f ▁ 7 , ▁and ▁was ▁made ▁by ▁the ▁firm ▁of ▁Tele phone ▁and ▁Standard ▁Time ▁( ), ▁later ▁called ▁Ten ovis . ▁A ▁not ew orth y ▁feature ▁was ▁that ▁when ▁the ▁clear - text ▁letter ▁was ▁key ed , ▁the ▁corresponding ▁ci pher ▁letter ▁could ▁be ▁sent ▁out ▁simultaneously ▁by ▁the ▁transmit ter ▁as ▁a ▁Mor se ▁character . ▁This ▁from ▁a ▁technical ▁point ▁of ▁view , ▁a ▁fairly ▁complicated ▁operation . ▁The ▁machine ▁thus ▁was ▁like ▁a ▁ci pher ▁tele pr inter ▁except ▁that ▁instead ▁of ▁the ▁ 5 - element ▁alphabet ▁the ▁ordinary ▁Mor se ▁alphabet ▁was ▁used . ▁The ▁maximum ▁key ing ▁speed ▁was ▁also ▁the ▁same ▁as ▁on ▁a ▁current ▁( 1 9 4 0 s ) ▁ci pher ▁tele pr inter . ▁It ▁could ▁not