Naval shells adapted as aerial bombs

How often were naval shells used as aerial bombs, and how did they compare with purpose-built bombs?

They were fairly widespread as expedient weapons, but purpose-built bombs were usually more effective.

Japan was not alone in adapting existing naval shells for aircraft use. Reusing a shell design was a widespread expedient when an air force needed bombs faster than a purpose-built weapon could be designed and manufactured. Purpose-designed bombs nevertheless offered better characteristics for aircraft delivery and target effect. Shell-derived weapons often demanded a steep dive or toss-bomb maneuver to strike and detonate as intended. The comparison shows the difference between quickly available ordnance and a weapon optimized for the new role.