Nowadays, ships have Internet access. While it is often cut off for reasons of operational security and for emission control, generally, the crew can send and receive e-mail and maybe make VOIP telephone calls.
It wasn't always that way. Formerly, the only way to make a call from a ship at sea was by the Military Affiliate Radio System (MARS). To make a MARS call, the ship had to have an amateur radio set and at least one member of the crew with an amateur radio license (or ham). That person had to be off duty. And since the amateur band was a high-frequency band, the calls could be monitored by almost anyone with a suitable HF receiver set, which included the Soviet Union. Making a MARS call pinpointed the ship's location to the Russians, so most of the time, the station was shut down.
That left good old snail mail for most communications. When a ship was overseas, the words "mail call" were the most welcome. If a ship had its schedule changed, the mail might not catch up for as long as a month. A month with no mail was a serious morale-killer; I have heard ship's captains on the secure satellite UHF net screaming at the shore duty pukes about the screwups in getting the mail to that captain's ship.
Mail call brought real news, if rather dated. At sea, the news arrived by a daily three-page radio message; try to think of what it would be like to cover all of the news of the nation and the world in three pages of text. Most stories were a headline and two sentences, if even that.
Sailors and their families who had experience at long deployments learned to consecutively number the outside of their envelopes. You knew if you were seeing a letter out of sequence that the letter may amplify details of a story you knew nothing about. I knew of one case where some wives were friends; one wife was visiting another and saw that her hostess had received her 56th letter from her husband while she had only received 14 letters. You can guess as to what one of the topics was of her next letter.
Telephone calls had to wait until the ship pulled into port. At that time, the most popular place to visit, other than the bars, was the European establishment known as a "telephone exchange." This was sort of like a post office, but with telephones. You signed in, giving your name, and the telephone number you wanted to reach. After waiting anywhere from a few minutes to four hours, you were directed to a telephone booth for your call, and you had better hope your party was home. Which is why most sailors tried to time their calls for when they knew their loved ones would be home (and probably asleep).
I knew one junior officer who received a letter from his wife which alluded to her being pregnant, but it did not specifically say that. She was too new at the game to know to number her letters. When liberty call was announced, he ran three miles to the nearest telephone exchange to make a call home. (She was indeed pregnant.)
Mail call also brought "dear John" letters, the letters which announced the breakup of a marriage or relationship. The favorite timing for the letters seemed to be roughly half-way through the deployment, giving the sailor at least three months to stew about it.
And if you wanted to see morale crushed, all you had to do was look at the faces of sailors who endured mail call after mail call with no letters, especially if they were married. That often was resolved with the spouse back Stateside receiving a visit by the Red Cross to make sure she (or he) was alive, and that almost always was followed by another "dear John" letter.
What happened when the ships got back are stories for another time.
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