Here are the following classifications for air tankers per the ICS system. The one above would be classified as a type IV. The biggest ones are classified as type I or II.
ICS-type I: 3000+ gal retardant
ICS-type II: 1800-2999 gal retardant
ICS-type III: 600-1799 gal retardant
ICS-type IV: 100-599 gal retardant
ICS-type I: 3000+ gal retardant
ICS-type II: 1800-2999 gal retardant
ICS-type III: 600-1799 gal retardant
ICS-type IV: 100-599 gal retardant