Throughout history, amphibious assaults have been among the most complex military operations, and had a success rate that was usually quite dismal. One fascinating aspect of World War II was the fact that few amphibious assaults, either Allied or Axis, failed.
The point of critical danger of an amphibious operation is not the first wave of assault troops. It is the buildup phase where the supporting arms and logistics still have not been landed. You have to get them ashore quickly before the defender can concentrate his forces upon you and defeat you. And one of the critical aspects of WWII assaults that helped them to be successful was the widespread use of naval gunfire to provide fires until such time as the ground forces artillery could be built up. Naval gunfire has the advantage of a very heavy weight of fire, combined with a very high rate of fire compared to conventional artillery.
The challenge is to provide timely control of those fires. Voice radio allowed units ashore to quickly nominate targets of opportunity, and observers ashore could control those fires. Well before WWII began, many cruisers and battleships carried their own float planes to spot the fall of gunfire. This was initially intended for long range gunnery duels with the enemy fleet, but it was obvious that they could also spot for fires ashore. Unfortunately, float planes operating over the assault beaches were quite vulnerable to enemy action, and losses were high.
The answer to that was to use either carrier based or shore based fighter aircraft to spot gunfire. In fact, for the invasion of Normandy, the US Navy created a special squadron equipped with Spitfires exclusively to support the gunfire mission. It was only operational for 20 days, but was an important tool in the gunfire support toolbox.
In the Mediterranean and European theaters, the Royal Navy provided a great deal of the gunfire support to Allied operations. While some of the vocabulary, and a few of the procedures, differ in minor details, the methods of control and gunnery are quite similar to the US Navy’s procedures, and even familiar to today’s gunfire support.