"Yesterday, December 7th, 1941 -- a date which will live in infamy -- the United States of America was suddenly and deliberately attacked by naval and air forces of the Empire of Japan." It was with these words that President Roosevelt asked Congress to declare war on Japan. I believe that the entry of the United States into World War II was inevitable and that the attack on Pearl Harbor hastened that entry.
The planes that the Japanese used would look similar to the ones shown above. Despite the rumblings that something was going on, the Americans thought that Pearl Harbor would be safe from attack. First of all, it was too far to the east and they didn't think the Japanese would risk their Navy that far from their homeland. Second, it was a fairly shallow harbor, so they didn't think they had to worry about aerial torpedoes.
For the first part, the Japanese maintained complete radio silence the moment they left Japan. Again, the Americans knew something was up because if I recall correctly, the Americans were aware the Japanese fleet had sortied. However, it was 1941 and it wasn't exactly easy to pick up something that size in the Pacific Ocean. Also if I remember correctly, the Japanese were able to follow a weather front almost entirely to Pearl Harbor.
For the second part, the Japanese were able to modify their torpedoes so that they didn't dive as deeply as other aerial torpedoes. Despite that, there were still some that were stuck in the mud of the harbor. After some analysis, it was discovered that they just put some lighter fins on the torpedoes.
The Japanese were able to damage all eight battleships in the harbor and sank four of them. Of these battleships, six of them would be repaired and later used in the war. One battleship, the USS Nevada was able to get underway but her Captain later beached her because he didn't want her sinking in the main channel and bottling up the harbor for future use. The USS Arizona was destroyed completely as a Japanese bomb was able to hit her magazine. She is now memorialized in the spot where she sank.
To this end, the Japanese lost 29 planes and some midget submarines. It was a complete tactical victory but some may argue was a strategic defeat because Japan could not sustain a war with the United States. They had hoped that the damage would be complete enough that they could establish a fortress in the Pacific and force the Americans to sue for peace. There were some in the Japanese military and government that did not follow this view and they knew their days were numbered...but like good soldiers, they carried out the orders.
On the Japanese side, Yamamoto had planned this attack so that we would have received a declaration of war before the first bombs hit Pearl Harbor. That didn't happen and he realized that we would be very upset. I don't think he was happy about those circumstances nor do I think he really wanted to go to war with the United States. He basically guaranteed about a six month run and he was pretty close to being correct.
Many people believe that the President allowed Pearl Harbor to get attacked. I for one do not believe this for a minute. One of the biggest supporting arguments for the conspiracy is that the American aircraft carriers. Despite what we learned later in the war, carriers were still a new tool. Battleships were still the primary Naval weapon and I do not think anyone would sacrifice those just to get in the war. Besides, Roosevelt's main beef was with the Germans, so a fight with Japan would not help that cause. In fact, if Germany had not declared war on the United States, he would have been hard pressed to declare war on them. Another thing that people point to is that we had intercepts of the Japanese radio traffic. Well intercepts are nice if you can read them. As I said above, we didn't break the Naval code until a couple months later and even then there were still issues.
This was meant to be more or less a history of the event. I work for a Japanese company and I hope that we have move along since this fateful day. I consider Japan to be one of our better allies these days and I have a great deal of respect for them.