Ship covers and cancellations offer a fascinating insight into Naval History of the United States. Events like Keel Layings, Christenings, Commssionings, De-commsisionings, Re-commissionings, sinkings, and a myriad of events during a ships life are and have been capture on mail and philatelic covers.  These are very collectible and serve as a concrete way in which to document the history of our maritime nation. You don't have to be or have been a Swabbie to appreciate Naval History.

As any sailor or soldier knows, very few things are more important than mail call.  After a lengthy period at sea, sailors have been know to stay on ship rather than go on Liberty in the hopes of getting one or more letters from home. As such, most but not all, US Naval ships have their own post offices, and set of post marks to process ship mail.  These ship cancels vary in design depending on the purpose of the marking. Some ship board postal clerks created their own fancy designs on occasion. All of which ads to the variety availalbe to the collector.

There are many different ways to collect Naval history or ship covers.

Philatelic Covers
Beginning in the 1930's the hobby of collecting different postmarks of the fleet. Some collectors would send blank stamped self addressed envelopes to the ship and request a cancellation. Others prepared fancy cachets for special events or days such as Navy Day, the Fourth of July, Christmas etc.  Some ships created their own cachets, with designs of the ship or of its namesake.  Typically these covers were collector created and did not carry any mail..  In addition to holdiays, events in the life of the ship were often memorialized.  There is a very wide array of covers that fit into this broad category.

Sailors Mail
Refers to actual mail sent from a Sailor, Marine or Officer on board the ship.  Sometimes there may not have a named ship cancel but rather just a handwritten return address.  This was particularly true during World War 2, where most ship mail was canceled with a US Navy Handstamp.  After all, the watch word during that perios was Loose Lips Sink Ships. A very real threat. Thus steps were taken to twart enemy intelligence by obsuring the ship and its location.  Nonetheless, much mail exists with the ship name on the cancel and even more with ship names in the return address.
While such covers often show more wear and tear, some colelctors prefer it as having been genuinely intended to convey mail.

Penalty Mail
Official mail from the Ship's Captain and other officers to Fleet Commands and other facilities generally did not require postage, and thus carried a penalty inscripton of various designs indicating that improper use of such preprinted envelopes was subject to a $300 fine. Thus such mail navy on other is called Penalty mail. In this case it represnt official correspondance which means it not only carried the mail, but did so on official business. Generally speaking these covers tend to be long business sized covers and definately on the drab side. Nonetheless these are considered the epitome of Naval Covers by some collectors.

Cancels
The canceling devices used aboard US Naval ships have been broken into 10 basic Types with two additional types under the Locy Classifying System.  Within these types there are a wide range of variations that are cataloged by the Universal Ship Cancellation Society.  Some collectors interested in just a few ships, or perhaps jsut thos ships from a specific period, say WWII or say the Vietnam era, or those who wish to specialize on Destroyers or Cruiser or some other hull type, may want to pay attention to the various types of cancels as they build their collections.  In addition to standard classifyable cancles a plethora of Fancy cancels exist.  These were usually prepared by the ship's mail clerk, and range from minor modifications to dramatic illustrations.  In additon to fancy cancels, many standard three bar and other cancellations would have words inserted into their killers. These were often used to indicate the ships current location, such as Pearl Harbor, of San Diego, or foriegn ports of call.  US Navy ships with Asiatic ports of call, particualarly China are currently in demand and tend to bring significantly more attention when offered on eBay.

Other
In addition to the above there are picutre post cards that might picutre one or more ships, as well as programs from offiical ceremonies like commissionings, etc. These are also collected and can add a great deal to a burgeoning ship cover collection.

Collecting Parameters
The novice ship collector is often overwhelmed with how many ships there are or have been in the US Navy.   Most collectors limit their collection to one or more areas of interest.  The most common focus, is the ships I sailed on, or my pa or grandpa did.  Someone that served on a submarine or a destroyer might expand their intersts to all submarines or destroyers. Some focus on specific events. For example many people collect all the ships that were at Pearl Harbor on 12/7/1941. While others collect the destoryers that made up the Famous Fifty that were lend to Great Britain in the lend lease deal before the US entered WWII.  Some memorialize those ships that were lost at sea either through combat or storm. There is no right or wrong way to collect.