The shell fired from the Yamato was indeed a beehive anti- aircraft shell.
Think of it as a very large shotgun round and you have the basic idea.
The 46 cm (18.1 in) Sanshiki Model 13 round weighed 2,998 lb and was filled with 900 incendiary tubes and 600
steel stays. The round was equipped with a delay fuze set before firing that detonated the shell at the set altitude;
on explosion, the steel stays and the incendiary tubes were ejected in a 20-degree cone forward, with the shell
fragments from the explosion itself further increasing the amount of debris. The incendiary tubes ignited about a
half-second later and burned for five seconds with 5 m (16 ft) long flames. Each of the incendiary tubes was a
90 mm long, 25 mm diameter hollow steel cylinder, filled with rubber thermite (phosphorus, vulcanized rubber,
natural rubber, stearic acid, sulphur and barium nitrate) and ignited through holes on both sides.
The rounds were similar to conventional shells, except for their wood-filled ogive and several layers of
assembled fragments.
Regards