Almost every time I see the acronym MRT used, somebody or bodies ask what it stands for. Even when spelled out, many rocketeers still don't know what it refers to. This was the name used, before the term HPR was coined, for high power rockets built from model rocket components. Back then there weren't heavy-walled cardboard, phenolic, or fiberglass tubes available. I knew the term, not because I built them in the day, but because I've read the history of LDRS. Here's a nice article by Chris Pearson, the organizer of LDRS-1.
LDRS-1 Sport Launch, 24-25 July, 1982, Medina, OH
(SNOAR). Three unofficial “events,” prizes to be awarded
(no national contest points). Contact: Chris Johnston,
26481 Shirley, Euclid, OH 44132; (216) 731-3839.
-From Model Rocketeer, May, 1982 Con Calendar
LDRS-1, previously appearing in this space has been
determined to include intentional amateur activity not
announced in the original notice sent to the Model
Rocketeer. NAR members are urged not to participate
-From Model Rocketeer, June, 1982, Con Calendar