Civil War Tokens like yours appeared in the early 1860s because there was a severe shortage of US government-issued coins. Regular cents of the era were strongly hoarded, so private individuals started making small copper coins to meet the demands of commerce. The government caught up eventually, and Civil War Tokens disappeared. CWTs are eagerly collected today.
The picture shows a CWT like the one you have. Many different political and patriotic themes appear on CWTs. For a coin in good shape, like the one in the picture, figure a retail value of $40 to $50 US dollars, sometimes twice those amounts depending upon rarity. Since yours has stains, is heavily toned, and because it is possibly difficult to read, it may sell for $20 to a collector. A dealer would buy it from you for about $5 to $10. Fully uncirculated CWTs are very rare and can fetch several $100s of dollars.
The web universe of CWTs centers at (where else?) CivilWarTokens.com. Here you will find plenty of examples and very knowledgeable people. There are nice collections at the UK Token Society, on AnythingAnywhere, and on flickr.
The inscription says in full 'The Federal Union - it must and shall be preserved'. The only pattern I know about with 'Army and Navy' and the 'shall be preserved' slogan has no date. If you have one with an 1864 date, I would be interested in seeing a picture. We can start an e-mail exchange if you use the Contact Us link at the upper left.
Go to eBay and do a search for Civil War Token. You will find many specimens for sale. The themes, inscriptions, and devices (pictures) are intriguing. Some typical inscriptions are:
IT MUST AND SHALL BE PRESERVED
ARMY AND NAVY
LIBERTY AND NO SLAVERY
THE FLAG OF OUR UNION
FOR PUBLIC ACCOMMODATION
NOT ONE CENT