'Type 99 was a very popular designation, and bascially could refer to anythingy designed or adopted in 1940.'
No, it was 1939, as Jim noted, as 1939 in the Gregorian calendar was 2599 in the Japanese imperial calendar.
And, it wasn't anything designed in a particular year, it was the year that it entered military service.
Additional examples, the Type 0 fighter, or Japanese Zero, which entered service in 1940. It got a hell of a lot worse later in the war, though, when another system was adopted on top of that system...
The old Japanese system of nomenclature used to use the then current emperor's name and a numeral designation equal to his years on the throne.
For example, the Arisaka 6.5mm rifle was the Meiji (emperor) Type 38 (years of his reign).
"The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza
Baby Jesus cries when the fat redneck doesn't have military-grade firepower.