In “our day” the M-79 was the good old ‘blooper.’
Of course there are various “M-79” weapons from various countries.
http://halo.wikia.com/wiki/M79_Multiple_Launch_Rocket_System
http://halo.wikia.com/wiki/M79_Multiple_Launch_Rocket_System
Our buddy, that was later modified into the M-203 to fit under the M-16: http://halo.wikia.com/wiki/M79_Multiple_Launch_Rocket_System