But Nords' Morse code flashcards? No way!
Back in the Evil Empire "good ol' days" of the Cold War, U.S. Navy submarine radiomen had to be able to copy at least 16 words per minute of CW and transmit something like 6 or 10 wpm before they could earn advancement to E-6.
Then you'd go to sea for 90-day patrols, copying this stuff continuously 24/7 for three months.
When your XO (USNA '71) could transmit CW good enough to joke with the other radiomen about your personal appearance and your ancestry, you stepped up your game. After all, I had a plebe year. Besides, I wasn't going to leave my Morse flashcards at home since my spouse already had her own set stored there for us to practice.
A few years later, when we all started spending our "peace dividend", I was on a different surfaced submarine transiting the maze of channels off the Canadian/U.S. border. A Canadian frigate pulled abreast and started transmitting flashing light, probably because he wanted to [-]trade insults[/-] enhance his interoperability with his allied counterparts. (Either that or they couldn't raise us on VHF Ch16.) Our CO called down from the bridge "Hey, XO, make sure we're logging this communications net!" which is CO-speak for "I have no idea what the heck he's saying, so you'd better be backing me up."
The XO looked around the control room and said "Can anybody read flashing light?" I had just gotten off watch and had plenty other things to do so I wasn't about to raise my hand. Luckily another enthusiastic submariner said "Sure, XO, I can do it!" He leaped onto the periscope, a sailor stood ready with his logbook & pen ready to record this vital tactical information, and our steely-eyed killer of the deep said: "Stand by to record: Dash! Dash! Dot! Dash! Dash! Uh, dot, no wait dash!"
After he'd been thrown off the conn, I was on the damn scope for over an hour.