Missile and missal are easily confused words.
The spell-check application of most word processing software programs would not catch a slip-up of these two words. Spell-check is looking for words that aren’t in its dictionary, and words that resemble words in its dictionary but are possibly spelled wrong. Spell-check isn’t perfect. It doesn’t know and can’t guess what word you wanted or what word you meant, it can only judge the words on the page. If you used words that are all spelled correctly, it gives you a pass anyway.
Autocorrect suggests words that start with the same letters. It’s suggesting what word you may want to save time, but quite often, its suggestions are pretty off base. They don’t help you out, but they do make you laugh.
Missile is a noun. It means a flying (or self-propelling) explosive weapon that detonates when it hits its target.
Missal is a noun. It means a book of readings and ceremonial scripts used by parishioners during Orthodox and Catholic masses.
The following story uses both words correctly:
Misaki went to mass with her friend Mischa. During the latter half of the service, she couldn’t keep up with the all the movements the parishioners made, so she stayed seated. Two small boys in the pew in front of her were playing. They were blowing spitballs like they were firing missiles at each other. They had created their ammunition by tearing off pages of the missal book, rolling them up, and wetting them with their saliva. Eww.