Radar control could sharpen both coastal attack and defense

What developing technology could have made attacking or defending a coast easier during World War II?

Radar-controlled gunfire could improve accuracy for both coastal batteries and attacking warships, making each side more effective and the operation more costly.

Radar-controlled gunfire could improve the accuracy of an amphibious attack. It could also make the coastal defenses more dangerous to approaching forces. Both sides could benefit, increasing the cost of the operation.