1940:

• "19 TEXAS 40" along top.
• At some point late in the numbering, the dies for the number 4 change.
• Passenger plate color: purple on white.

• "TEXAS 1941" along top.
• Bus plates introduced.
• Passenger plate color: yellow/orange on black.

1942

• "TEXAS-42" along bottom.
• "Y" serial letter used after A,F, K, N, & V.
• A program was begun to recycle old license plates for the war effort.  This is perhaps part of the reason why pre-WWII Texas plates are much more difficult to find than many other states.
• Passenger plate color: black on yellow-orange.

1943-1944:

• As in many states, plates were not issued to conserve metal for the war effort. Thousands of old plates are collected & melted down.
• 1942 plates were to be revalidated with a 1943 windshield sticker, but the program was killed.
• Instead, 1942 plates were revalidated with small metal tabs for 43 & 44. 
• These tabs featured a 2-letter prefix which continued on plates through 1955. The prefix is serial, not a county or type code.
• 1943 tab color: yellow-orange on black.
• 1944 tab color: cream on green.

• New plates issued singularly due to continuing metal shortage.
• "TEXAS-45" at top.
• Plates were a more square shape, with a two-letter "stacked" prefix followed by 1 to 4 numbers.
• "Truck" & "Truck Tractor" plates replace Commercial.
• "Farm Truck" plates replace "Farm".
• Passenger plate color: black on yellow-orange.

• Slightly bigger plate with "TEXAS-(date)" at top (even yrs.) or bottom (odd yrs.) through 1950.
• Passenger plate color: cream on black.

• A delivery problem caused a plate shortage, so 1946 plates were revalidated with a 1947 windshield sticker that expired on July 15. (I do not believe any of these stickers are known to still exist).
• Eventually the new plates were issued, in pairs again.
• Passenger plate color: white on black.

• Exempt plates become permanent and no longer have an embossed year.
• "House Trailer" plates introduced. "Side Car" plates discontinued.
• Passenger plate color: yellow on black

1949: 

• Passenger plate color: black on yellow-orange.