Due to the Washington Treaty restrictions a Kaga class battleship was converted into an aircraft carrier. The Amagi was destroyed in an earthquake in September 1923 and it's design was used for the Kaga.
Initially the funnels discharged out the stern but this interfered with air operations. There were also three flight decks in the front.
There were four oil sprayed coal and eight oil fired boilers initially.
The exhaust went through 300' long tubes that went under the flight deck on each side.