The Kyushu Q1W "Tokai" (Lorna) was the only anti-submarine patrol aircraft that was ever put into production by the Japanese. The very first prototype was designed by Nojiri Kozo completed in December 1943 and was followed by eight more prototype and pre-production aircraft. From the beginning, there were no problems but the position and the area of the tail were slightly modified to improve stability when flaps were used. Production started immediately from April 1944 before the type was even officially adopted by the Navy in January 1945. Apart from the first nine, a further 149 "Tokai" were delivered.
Production by year
1943 - 7
1944 - 88
1945 - 58
Total - 153
In September 1944 an order was given to replace the Type 92 7.7mm machine gun with one fixed 20mm cannon, with 100 bullets, positioned under the fuselage, near the wing root*. The aircraft equipped with 7.7mm machine gun were designated Q1W Model 11 and those with the 20mm cannon became Q1W1a Model 11ko. The mass production order for the Q1W1a was given in February 1945.
Around that time (February 1945) another order was given to remodel the first and second prototypes to include twin controls and become trainers, designated Q1W1-K, to train pilots for the Yokosuka P1Y "Ginga". The Q1W1-K was officially adopted in July 1945.
A final variant was an all-wood trainer version designated "Shisei Tokai-kai Renshuki" (Experimental Tokai Remodelled Trainer) that was developed by Kyushu following an order given on April 1945. The prototype was built by "Kurashiki Koku Kako" (Kurashiki is a municipality in Okayama prefecture, Aviation Chemicals) with wooden wings, tail and rear fuselage but the War ended while it was undergoing strength tests.
In the photo below one of the "Tokai" prototypes or pre-production aircraft in overall orange as indicated by the hinomaru with white surround.
*Encyclopedia Vol.VIII and Akimoto (All the Regular) agree that "Tokai" had only one 7.7 rear firing machine gun which was replaced by a downward firing 20mm cannon in the Q1W1a version. Nohara in Green Arrow's X-plane mentions a combination of 7.7 mg plus a 20mm cannon for the Q1W1a. "Aireview's" 1972 book mentions too the 7.7mg plus one 20mm combination and curiously mentions that "late production aircraft were equipped with two extra 20mm cannons in the nose" but forgets to mention it again in the a/c's data table on the next page. Francillon mentions one or two 20mm in the nose.
Personally I trust Encyclopedia and Akimoto who are more precise at the position of the cannon and the designation of the particular model.