Shawl Collars on Tailcoats?
Tailcoats are stunning. Not sure why I adore tailcoats. But you could always wear the Evening Cape if the shawl collar isn't working for you. The evening cape is a black sleeveless garment of all-wool gabardine, barathea, elastique, broadcloth, or beaver. The cape lining is ultramarine blue. It is for wear with either mess dress or formal evening dress uniforms, and is worn with the black dress cap and white dress gloves. Length will be no longer than 2" below the knee.
Never seen US or UK military in tails. Both traditionally use jackets as shown here for formal occasions - something like a tail coat with the tails removed, known in the UK as mess kit and I've seen them called Spenser jackets. Looks good to me!