This details how to repair this toy when it fails to work when charged.
1. First remove the screw at the bottom of the submarine.
2. Remove the top and bottom centre halfs
3. This is the difficult part using a pair of pipe wrenches slowly squeeze round the nose of the submarine quite hard to break the glue joining the nose assy on.
4. Then remove the nose exposing the circuit inside.
5. I found that the batteries were charged but the connector used to charge the sub had corroded and with the charging plug remove the switch in the the connector to turn on the sub was not making contact.
6 With the connector replaced the sub should operate normally.