Japanese Navy RED Cipher machine
The US Navy captured this Japanese RED cipher machine. Like its diplomatic counterpart, the Navy machine separated the alphabet into two subgroups. However, instead of using the Romanized spellings, it has a katakana keyboard. It is believed that due to the difficulty in using and maintaining this machine, the Navy RED saw little use by the Japanese fleet.
Source: National Cryptologic Museum
The prototype machine was finally completed as 91-shiki injiki(九一式印字機) ("Type 91 print machine") in 1931. The year 1931 was year 2591 in the Japanese Imperial calendar. Thus it was prefixed "91-shiki" from the year it was developed.
The 91-shiki injiki Roman-letter model was also used by the Ministry of Foreign Affairs as Angooki Taipu-A (暗号機 タイプA) ("Type A Cipher Machine"), codenamed Red by United States cryptanalysts.
The Red machine was unreliable unless the contacts in its half-rotor switch were cleaned every day. It enciphered vowels (AEIOUY) and consonants separately, perhaps to reduce telegram costs, and this was a significant weak point. The Navy also used the 91-shiki injiki Kana-letter model at its bases and on its vessels.