>>> replace each letter in 'ABCDEFGHIJKLMNOPQRSTUVW' with the corresponding NATO Phonetic alphabet code

- elapsed 1.733 seconds -
nato = 'Alpha Bravo Charlie Delta Echo Foxtrot Golf Hotel India JULIK Mike November Oscar Papa'
'ABCDEFGHIJKLMNOPQRSTUVW'

def replace(seq, a, b):
    return ''.join(b[i] if i < len(b) else i for i in [b.index(c) if c in b
        else len(b) + c - 1 for c in seq])
print(replace(nato, 'ABCDEFGHIJKLMNOPQRSTUVW', '123456789101112131415'))