I am puzzled by this. Why is "aircrafts" invalid, while "crafts" can be used legitimately? I've also heard that "crafts" cannot be used because the plural of "craft" is always "craft". Which is right?
"Craft" is one of those words that has several very different meanings.
"Craft" could mean "skilled work" or "hobby". In this case, the plural is "crafts" - such as in "arts and crafts".
"Craft" can also mean a vehicle that people use to travel through water, air, or outer space. In this case, the plural is "craft" (no 's') - such as in "aircraft", "watercraft", or "spacecraft".
Here's an explanation for why this is:
Use for "small boat" is first recorded 1670s, probably from a phrase similar to vessels of small craft and referring either to the trade they did or the seamanship they required, or perhaps it preserves the word in its original sense of "power."
So, it sounds like we have the British Navy to thank for this confusing usage.
I think there is a distinction to be drawn here which will allow you to avoid confusion; namely: the noun "craft" has several meanings, while "aircraft" has only one.
The meaning you are focused on is "craft" as a moving vessel, such as watercraft, aircraft, or spacecraft. All three of these terms as well as "craft" itself are the same in their singular and plural forms, like the word "deer."
Three craft were in the water, two in the air.
However, "craft" also means "an activity involving skill in making things by hand." When the word is used with this meaning, it is pluralized normally:
- That potter really knows his craft.
- His two crafts were cabinet making and bricklaying.