so Amagi and Tosa are what Akagi and Kaga were originally going to be as battleships?
Well, not quite right... Amagi and the Tosa were going to be the first ship of their respective class, the second ships are supposed to be Akagi and Kaga respectively. Tosa was cancelled due to washington naval treaty, and was scuttled. Amagi was broken due to great kanto earthquake. Akagi and Kaga converted to Carriers.
Btw,i wrote this on phone, don't have time to check the source, if i'm wrong feel free to correct me.
Well, not quite right... Amagi and the Tosa were going to be the first ship of their respective class, the second ships are supposed to be Akagi and Kaga respectively. Tosa was cancelled due to washington naval treaty, and was scuttled. Amagi was broken due to great kanto earthquake. Akagi and Kaga converted to Carriers.
Btw,i wrote this on phone, don't have time to check the source, if i'm wrong feel free to correct me.
And originally it would've been Amagi that was completed as an aircraft carrier. When she wrecked by the Great Kanto Earthquake, the third and fourth ships of the class (Atago and Takao, not to be confused with the later heavy cruisers of the same names) weren't sufficiently far along in construction to substituted for her. This left Japan in a bit of a bind, since the two capital ships allowed for conversion into carriers under the Washington Treaty were allowed to be 6000 tons heavier than other carriers. The IJN was already outraged at being limited to a smaller navy than the US and UK, so there's no way they'd allow the US Navy to get two 33,000 ton carriers while the IJN only got one. But Tosa and Kaga had already been launched, and while their hulls weren't ideal (being shorter and wider than the Amagi class) there weren't any others on hand of sufficient size. So they could pick one to make into a carrier and the other to dispose of, and for whatever reason Kaga was the lucky one. Until Midway at least.
Honestly, given all the outright cheating Japan later did with regard to treaty compliance, I'm surprised they didn't just build a copy of the converted Akagi and insist that it was Amagi.