two robot grain ships
A grain ship was a type of freighter specifically used to carry loads of grain. The Antares-types' NCC-G1465 and NCC-61465 were examples of this kind of vessel. (TAS: "More Tribbles, More Troubles")
In 2268, Sherman's Planet awaited a shipment of quadrotriticale held at Deep Space Station K-7. At the time, the USS Enterprise was held responsible for protecting the grain until the shipment could be taken to the planet. (TOS: "The Trouble with Tribbles")
The following year, the Enterprise escorted two robot grain ships to Sherman's Planet, after it had been struck by crop failures and famine. (TAS: "More Tribbles, More Troubles")