Notes:
This was the only use of the obverse die.

The reverse die of this variety was also used on:
Vlack 13-78B

Attribution points:
Only two 1778 reverses exist in the Machin's Mills series: 78A and 78B.  On the 78A reverse, the staff points to the 7 of the date; on the 78B reverse, the staff points to the 1 of the date.  Also, note the position of the small "tree" relative to the A of BRITAN.

Great Britain did not strike any Halfpennies in 1778.

Images courtesy of Jack Howes

Sources and/or recommended reading:
"Walter Breen's Complete Encyclopedia of U.S. and Colonial Coins" by Walter Breen