A company that’s bankrupt and closes is said to have “gone under” (as if buried). There are several submarine (“sub”) sandwich shop jokes.
 
“The inventor of the submarine sandwich is unknown, for example, because his little shop soon went under” was printed in a 1983 newspaper. “Oct.  7, 1898   The first submarine sandwich was introduced, but the company went under” was posted on the newsgroup novell.community.chat on November 22, 1999. “The first submarine sandwich shop opened in 1898, but the store went under” was posted on Twitter on December 1, 2014.
 
“My diving school has gone under” is a similar joke.
   
   
2 September 1983, Longview (TX) Morning Journal, “Lesser-known inventors deserve more recognition” by Van Craddock, pg. 4-A, col. 3:
THE INVENTOR OF THE submarine sandwich is unknown, for example, because his little shop soon went under.
     
Google Books
A Treasury of Victorious Women’s Humor
By James E. Myers
Springfield, IL: Lincoln-Herndon Press, Inc.
1999
Pg. 220:
The turn of the century saw the first submarine sandwich. The company went under, unfortunately.
 
Google Groups: novell.community.chat
Some minor punishment
Felton Green
11/22/99
(...)
Oct.  7, 1898   The first submarine sandwich was introduced, but the company went under.
     
Google Groups: Sailor’s Adult Humor
Saturday p.m. AHumor
stewburner
10/19/08
(...)
The first submarine sandwich was introduced in the late 1800’s. Wouldn’t you know it? The company went under.
 
Twitter
PuterPrsn™
@PuterPrsn
In 1898 the first submarine sandwich was introduced, but the company went under. #pun
9:11 PM - 23 Jun 2009
     
Miami (FL) New Times
Friday Food Funnies: Silly Stuff
LEE KLEIN | JULY 3, 2009 | 7:00AM
(...)
Did you hear about the submarine sandwich shop? It went under.
 
Twitter
Deborah Austin
@DebsSweet
The first submarine sandwich was introduced in the late1800’s. Wouldn’t you know it? The company went under.
4:09 PM - 16 Aug 2009
 
Twitter
Michael Du Pont
@MikeDComedy
I applied for a job at a Submarine Sandwich shop. but it went under.
1:05 PM - 7 Mar 2012
 
Twitter
Bernard Cormier
@BernardCormier
Pun of the Day (# 281 of 366): On Oct. 7, 1898, The first submarine sandwich was introduced, but the company went under. #SJPuns
6:30 AM - 7 Oct 2012
 
Twitter
A-A-Ron
@goulden_eye
My submarine sandwich business went under. Hoping it will resurface soon!
9:31 AM - 6 Feb 2013
 
Twitter
Joshua C. Day
@JoshDayComedy
My submarine sandwich shop went under #DownBusinessPlanScope
1:27 PM - 7 Jun 2014
 
Twitter
Mike Clark
@writermike
After the first submarine sandwich was introduced the company went under. – various sources
9:41 AM - 27 Jul 2014
 
Twitter
TG
@TonyEdGaber
The first submarine sandwich shop opened in 1898, but the store went under.
9:42 AM - 1 Dec 2014
 
Twitter
Gary
@Oklahomakid777
The first submarine sandwich was introduced, but the company went under.
7:40 AM - 7 Oct 2016