Popeye tells fellow deep-sea diver Bluto of a sunken treasure. Popeye says they’ll split the treasure 50-50, but Bluto knocks Popeye out and steals the treasure map. Popeye comes to and heads for the treasure on his own (albeit with Olive Oyl in tow).
Popeye and Bluto go back-and-forth underwater. Bluto tries to trap Popeye in a giant clam, but Popeye sends a signal up to Olive, who funnels down some spinach to him. Popeye subdues Bluto and hauls up the treasure chest. When Bluto comes back up and demands his half of the treasure, Popeye breaks the chest in two and knocks Bluto over the head with his half.
The mechanical nature of most of the gags, and the lack of music in the underwater sequence, render this a decidedly average Popeye cartoon.
On a rating scale of 1 to 4 spinach cans, I give this cartoon: 
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