Important Note: Many other excellent timelines are available online regarding the history of cryptography or WW2, including the NSA pre-1952 Historical Timeline

Information is from a variety of sources. Military information is primarily from the timeline at Wikipedia

Year Date Int’l/Military U-Boat Cryptologic Dayton
1860       first US patent for cryptographic device granted  
18??         John Patterson founds the national cash register Company
1914     At the start of World War I, Germany had 48 submarines of 13 classes in service or under construction;
in their initial campaign in the North Atlantic, German U-boats had sunk nine warships while losing five of their own number
1919   Part V of the 1919 Treaty of Versailles had imposed severe restrictions on the size and capacities on the armed forces of the Reich. In regards to the Navy, Germany was allowed no submarines, no naval aviation, and no battleships   Hugo Koch, a Dutchman, comes up with the idea for the Enigma cipher machine; Damm receives Swedish patent for cryptoraphic device using “rotor” (Deavors, p. 5_)  
1921       William Friedman goes to work for the Army Signal Corps  
1923       Arthur Scherbius produces an Enigma machine for the commercial market  
1924 January     Lt. Laurence Safford takes the head of the Reseach Desk at the US Navy Codes and Signal Section (later became Op-20-G)  
1925       First US Navy radio intercept station set up on Guam followed by two in the Philippines and one in Shanghai  
        Joseph Rochefort assigned to the Research desk  
1928 July     The "On the Roof Gang" begins training on the roof of the old Navy Department.  
1930 April     William Friedman authorized to hire three junior cryptanalysts to begin a bureau known as the Signal Intelligence Service  
1931       Japanese cryptographers begin use of an "unbreakable" cipher called "Red" produced by a machine using rotors with a complex wiring arrangement  
1932       In Poland, Marian Rejewski recovers wiring of Geman military Enigma rotors  
1933 1 October   Unterseebootsabwehrschule founded.    
1935 29 June   The Anglo-German Naval Agreement (A.G.N.A) of June 18, 1935 was a bilateral agreement between the United Kingdom and German Reich regulating the size of the Kriegsmarine in relation to the Royal Navy; the launch of U-1    
  27 September   I.Unterseebootsflotille Weddigen commissioned by its first chief, Fregattenkapitän Karl Dönitz    
1936       Red system broken by US Navy  
1936 1 January   The appointment of Kapitän zur See Karl Dönitz to the post of Führer der Unterseeboote    
1937       Introduction of the Purple Japanese cipher machine  
1938 April       Harry Williams, at the request of Col. Edward A. Deeds, President of the National Cash Register Company, hired Joseph R. Desch to begin NCR’s Electrical Research Laboratory
1939 15 March   Germany invades Czechoslovakia

  1 June     The Japanese naval code JN-25 introduced  
  1 September Germany invades Poland      
  3 September France and Britain declare war      
1940       By the summer of 1940, through the collaboration of the staff of William Friedman of the SIS and Lt Safford Japanese diplomatic traffic was easily read  
  14 March     First bombe operational at Bletchley Park  
  summer Battle of Britain      
  September     Japanese Purple cipher broken by US Army; first JN-25 decrypts by Op-20-G  
  October 2       Joseph Desch writes in December to Dr. George Harrison of the NDRC that on October 2nd his laboratory staff–Mr. Robert Mumma and Mr. Louis DeRosa–are beginning work on the development of high speed electronic counters.
1941 March      

The National Defense Research Committe appoints Joseph Desch an "Official Investigator" and requires him to sign the first of a series of pledges of secrecy

1941 9 May U-110 captured intact by the British (Williamson, Wolf Pack)      
1941 June     Joseph Rochefort takes command of the radio intelligence unit of the 14th Naval District in Hawaii, renaming it the Combat Intelligence Unit  

Desch’s lab develops a counting bank, using his thyratron tubes, capable of counting at 1,000,000 impulses per second (1 MH in today’s terms). Desch presents a talk on this topic in December at an Electronic Counter Conference in Washington. George Harrison of the Instruments Section of the NDRD later write Desch that his talk was "quite effective".(NCR Archive)

1941 15 November   Launch of U-459, the first Type XIV tanker U-boat, or so-called Milchkuh (Williamson, Wolf Pack)

1942 13 January   Operation Paukenschlag offensive against shipping off the American coast begins. The start of the second “Happy Time” (Williamson, Wolf Pack)

1942 11 February   The Scharnhorst and Gneisenau and Prinz Eugen rush out of Brest through the English Channel to northern ports, including Wilhelmshaven, Germany; the British naval units fail to sink any of them.    
1942 March       US Navy and National Cash Register Company sign a contract to develop and construct specialized machines. This contract establishes the Naval Computing Machine Laboratory (Wilcox, The Cryptanalytic Bombe)

1942 8 May In the Pacific theater, the Battle of the Coral Sea comes to an end. This is the first time in naval history where two enemy fleets fought without seeing each other. In addition to the loss of the Lexington the Yorktown is badly damaged; it returns to Pearl Harbor for repairs.      
1942 June   More than 600,000 tons of shipping were sunk (Budiansky, Battle of Wits, p. 236). This was close to Admiral Doenitz’s goal of 700,000 which he felt would cripple Britain


1942 18 June Manhattan Project begins; Churchill arrives in Washington for meetings with Roosevelt      
1942 September 4     US Navy approves the plan for bombe construction (Budiansky, p. 343)  
1942 December   The total figures of Allied losses during 1942 in the Atlantic: 1,664 ships, of 7,790,691 tons. U-boats alone sank 1,160 ships and 6,226,215 tons.(Parrish, The Ultra Americans)

1943 14 January Casablanca Conference of Allied leaders begins. Churchill and Roosevelt discuss the eventual invasion of mainland Europe, the invasion of Sicily and Italy, and the principle of unconditional surrender      
1943 April     WAVES begin arriving by train at Union Station in Dayton to report for duty at the US NCML.  
  May 2     First two US Navy bombes at the USNCML begin tests (Budiansky, p. 343)  
  31 August     first US Navy bombes arrive in Washington (Budiansky, p. 344)