If you send many Christmas cards, this is the time of year when several are returned to you because of an out-of-date address. In the United States, the average person moves 11.7 times in a lifetime, so maintaining an accurate address list is a never-ending task.

Although people move, the addresses do not. You probably don’t address your Christmas cards to “Occupant” at a particular address, but if you did, you wouldn’t have to deal with as many returned envelopes. Imagine the nightmare of addresses that moved as much as people do.

That brings us to ZIP code 48222. It may not be quite as mobile as your college roommate, but it certainly isn’t stationary. In fact, it isn’t in the same place it was when you started reading this article. That’s because 48222 is assigned to a boat that is floating on the Detroit River.

The JW Wescott II is a 70-year-old boat that makes its home in the Detroit River. There is little about its appearance that is remarkable. It has a 14 gross tonnage volume, is 45 feet (14 meters) long with a top speed of 15 knots. Compared to the other vessels that navigate the Great Lakes waterways, it isn’t the largest, fastest, or prettiest. It is, however, the only one that has its own ZIP code.

The boat is named after John Ward Westcott (1848-1913). He became captain of a steamer at the age of 20 years, becoming the youngest captain on the Great Lakes.

In the 1870s, Wescott saw the need for improved communications between ships. The process for a ship’s captain to receive orders and send replies was cumbersome, generally requiring the ship to dock while messages changed hands. This consumed valuable time that could better be put toward improving the speed of delivery of the ship’s cargo.

Wescott established a marine reporting firm in 1874. His boats, smaller and faster than the cargo ships, could meet the ships and facilitate communication with greater ease and efficiency.

It was at this time that Wescott added an additional service. He helped the crew members of the ships stay in touch with family and friends by passing along messages to and from family and friends. He charged 25 cents per item — significantly more expensive than the post office would charge. Customers were more than willing to pay for the service, however. Unlike the post office, Wescott did not require seafaring patrons to come ashore to find him; he went directly to the ships. Wescott’s boats — frequently as primitive as rowboats — pulled up next to a much larger vessel, received a bucket lowered on a rope, filled the bucket with messages and parcels, and went on to its next customer. This service came to be known as “mail in a pail.”

Wescott’s business did well enough, serving the many vessels that sailed past Detroit in the late 19th and early 20th centuries. It was when the motor industry came to Detroit that things really took off, however. The Detroit River became one of the busiest waterways in the world, with massive freighters carrying raw materials, supplies, and merchandise. These giant vessels stood to lose a substantial amount of profit by taking the time to dock for something as trivial as a mail call. For this reason, Wescott’s business boomed.

In 1948, the JW Wescott Company contracted with the U.S. Postal Service to become an officially-sanctioned mail delivery service. Its primary vessel, JW Wescott II, also became “an official US Postal Service boat.” Anyone wanting to send a message to Myron Schmohopper, a crewmember on the freighter Dawn Treader, need only write, “Myron Schmohopper, USS Dawn Treader, Marine Post Office, Detroit, Michigan” on the envelope. For the cost of one postage stamp, the message would be delivered.

About 15 years after the JW Wescott II became an official mail boat, the U.S. Postal Service introduced the Zone Improvement Plan (ZIP) code system. Every mail sorting and delivery center in the USA was assigned a ZIP code. Since JW Wescott II was an official mail sorting and delivery center, logically, it needed a ZIP code, too.

That is how this little boat in the Detroit River ended up being designated with ZIP code 48222. Technically, that ZIP code belongs to the Detroit River Station Post Office, but that is currently in the form of the JW Wescott II. Now, if you want to write to the aforementioned Myron Schmohopper, you need to add “48222” to the end of the address. This allows the US Postal Services to use state-of-the-art computers to scan the number, automatically sort the mail, and speed it to the Wescott, where it continues to be delivered with the 19th-century “mail in a pail” system.

The unofficial motto of the Postal Service is “Neither snow nor rain nor heat nor gloom of night stays these couriers from the swift completion of their appointed rounds.” They should also add, “nor the sinking of our mail boat.” On October 23, 2007, the Wescott was delivering mail and a Canadian pilot to a 533-foot Norwegian oil tanker when it started to take on water. The mail boat listed on its port side. Twenty seconds later, it was gone. Two of the Wescott’s crew were killed. Despite the tragedy, six days later the vessel and deceased captain were retrieved from the bottom of the river. The body of the other member of the crew was never found.

The JW Wescott II was repaired and restored to service. It continues to operate in the waters near the Ambassador Bridge, linking Detroit to Windsor, Canada. It continues with its mission to deliver the mail, but it has kept up with the times. It also delivers Amazon shipments, groceries, and personnel. It never stays in one place, but unlike your neighborhood post office, it delivers the mail 24 hours a day, seven days a week.