This brand's best known engine was the "Type 91" 12-cylinder W-engine that was derived from the Napier Lion. Its engines were between 500 hp and 750 hp. They were mounted on the Aichi EIIA, Mitsubishi G3M aircraft, etc.

-There was a Hiro V-12 on the H2H aircraft. There was the "Type 94" as well, but with 1,180 hp.

-Hiro's activity in the manufacture of aviation engines began at the beginning of the 1930's

-Hiro was the place where the 11th Air Naval Arsenal was located, and these engines that were built there were known by this name.

“RO.2”

-Another stellar moment of this brand was already in WWII when it was entrusted with the responsibility of developing the RO.2 rocket engine, an equivalent to the German Walter 509A.

-This liquid-fuel rocket engine was known as the Toko RO.2 with a thrust of 1500 Kgf.

This engine was intended for the Japanese Me-163, the so-called "Shusui".

-It used exotic fuels, different from the Germans, for example the Ko-Liquid was like the T-Stoff, with 80% hydrogen peroxide but with "oxyquinoline" and "pyrophosphate" as stabilizers.

-The Otsu-Liquid, was the C-Stoff but with 30% hydrazine hydrate in methanol with a small amount of copper potassium cyanide.

“Schematic drawing for the Walter engine”

-Above we show a schematic drawing for the Walter HWK 109-509A1, from which the RO.2 is copied.

From Appendix A6/6: The most famous Hiro engine was the Type 91 (12W), but there also were the Type 94 and the Type 61.