The Battle of Grand Gulf was fought on April 29, 1863, during th: There is complex dialectal variation in words with the open front and open back vowels /æ ɑː ɒ ɔː/. These four vowels are only distinguished in RP, Australia, New Zealand and South Africa. In GA, these vowels merge to three /æ ɑ ɔ/,[172] and in Canadian English, they merge to two /æ ɑ/.[173] In addition, the words that have each vowel vary by dialect. The table "Dialects and open vowels" shows this variation with lexical sets in which these sounds occur.