These are depth charges as utilized by the Grand Army of the Republic. Depth charges functioned as weapons of underwater combat, designed with the purpose of inflicting damage or achieving the destruction of submarine vehicles and personnel. Their detonation occurred upon making contact.
In 32 BBY during the Invasion of Naboo, OOM-9, a B1 battle droid, gave the command to deploy depth charges within Lake Paonga. The objective was to dislodge the Gungans from Otoh Gunga, their underwater city.
During the Battle of Mon Calamari, the Grand Army of the Republic employed depth charges against Separatist forces operating underwater.