“It it ain’t raining, we ain’t training” is a saying that began in the United States military, showing that troops are ready to go in even the worst conditions. “The Camp Lejeune (‘If it ain’t raining, we ain’t training’ ) Marines” was cited in print in 1991.
 
The saying has also been used in athletic training, often with the military’s “we” changed to “it.” “After all, if it ain’t raining, it ain’t training” was cited in 2003. “You know what we say in the Army: If it ain’t raining, you ain’t training” was cited in Runner’s World in 2003.
     
 
Google Books
Marines
Division of Public Affairs, Media Branch, HQMC
1991
Pg. 148:
With the sun shining brightly and temperatures climbing towards the 70s, the Camp Lejeune (“If it ain’t raining, we ain’t training”) Marines wait for Murphy’s Law to kick in. And it does.
     
Google Books
Film Review Special: Yearbook
Visual Imagination Limited
Issues 25-35
1999      
Pg. 19:
“It was like Captain Dye had booked the rain especially. He’d say: ‘If it ain’t raining, you ain’t training. If it ain’t snowing, we ain’t going!’”
 
Google Books
All You Can Be:
A Soldier’s Reflections on Service in the Greatest Army the World Has Ever Seen
By James David Kay
Puyallup, WA: Valley Press
2000
Pg. 242:
They have a saying in the Army that goes like this, “If it ain’t raining, we ain’t training.” Spend any amount of time in Europe, Hawaii, Korea, or Fort Lewis, Washington, and you’ll see a fair amount of rain.
   
Google Books
Panzer Leader and the Red Menace
By Robert Von Cocktail
Authorhouse
2003
Pg. 74:
A typical March dusk in the Federal Republic; ideal for military training exercises. After all, if it ain’t raining, it ain’t training.
     
Google Books
Runner’s World
2003
Pg. 93:
“You know what we say in the Army: If it ain’t raining, you ain’t training.”
 
Google Books
Absolutely American:
Four Years at West Point
By David Lipsky
New York, NY: Houghton Mifflin Company
2003
Pg. 158:
It’s been a wet summer, the smell of mud as pungent as in a greenhouse. (The new cadets have picked up the traditional Army salute to poor weather: “If it ain’t raining, we ain’t training.”)
   
Google Books
A Democracy is Born:
An Insider’s Account of the Battle Against Terrorism in Afghanistan
By Matthew J. Morgan
Westport, CT: Greenwood Publishing Group, Inc.
2007
Pg. 139:
The U.S. Army infantry have a saying, “If it ain’t raining, we ain’t training,” and soldiers will often revel in hardship created by the natural elements.
       
Google Books
The Unforgiving Minute:
A Soldier’s Education
By Craig M. Mullaney
New York, NY: The Penguin Press
2009
Pg. 50:
As we spent nights marching through torrential thunderstorms, officers urged us on with motivational cheers. “Nothing but a little Ranger sunshine, cadets.” “If it ain’t raining, we ain’t training.” “You gotta love being cold, wet, and miserable. Love the Suck, men, love the Suck.”
 
Facebook
Organic Fitness and Training
Words proclaimed during my last class, “If it ain’t rainin’, we ain’t trainin’!” - former marine and dedicated O.F.A.T. trainee. Thanks loyal O.F.A T. crew for making me a part of your health and wellness goals in 2014! Farewell for now. Keep kicking a$$ in 2015! - Trainer Alina — with Amy Ramm and Jim Rodman.
January 9, 2015
 
Twitter
Ed Melancon
‏@edtheplumber
If it ain’t raining, it ain’t training. (at @HappysRunning Club in Baton Rouge, LA) https://www.swarmapp.com/c/jnQ4nUU0AIb
5:43 PM - 10 Mar 2015