Spruance's battleships as the fallback at the Philippine Sea

Were Spruance's battleships intended for a great gun battle at the Philippine Sea, or as insurance if the carriers failed?

They were the fallback force; if carrier aircraft could not stop the Japanese, the battleships would have to protect the carriers by fighting.

The viewer asks whether Admiral Spruance actually expected a climactic surface action or was preparing for carrier aviation to fail. The battle line was the backup option. The carriers could not be risked in a close encounter if their air groups failed to stop the approaching enemy. In that emergency, the battleships would have to interpose and fight regardless of how unattractive the exchange looked.