A 1925 Japanese collection of official papers, which was sent to Kawasaki, mentions a Do. Q aircraft as a submarine-carried aircraft.
The first paragraph reads, roughly:
"To their request, regarding the work progress of the Do. Q - (machine with Siemens motor), [would] like to share with them [Kawasaki?] that we will be expecting such a motor from the delivery company and then try to make it [Do. Q]. We assume that with this engine, a better performance of the Do. Q will be achieved."
The second paragraph:
"[As far as] flying the Do. Q, built [using the] Le Rhone engine is concerned, it was executed some time before another flight with the maximum payload. The engine of the [Do. Q] started effortlessly in 20 seconds, however, the speed [was] very low, which was detected by [comparison to the Dragonfly (Do. A)] and it found that the rate [speed?] of the Do. Q was [inferior] to the Dragonfly. Also on the water, the rotating mass of the motor [required] that the turn down the Le Rhone engine [to] only 800 [Touren?] and the pilot is forced to temporarily turn off the ignition to the engine. The consequences of this is that the boat [was] pretty jerky and restless and rolls up after turning the ignition [on]. The flight tests were, therefore, with the Do. Q [using the] Le Rhone."
"So we must ask them [Kawasaki?] to be patient in this affair, until we try our exports [engines] with [the] built-in Siemens motor [as we regret that opposition to ] the Le Rhone engine [has] stiffened. It will be understandable to them that the Do. Q [will] only achieve good results and for this reason [we must]refrain from [using] the Le Rhone engine.