1. "Miss Former Battleship" - Kaga was originally built as one of two Tosa-class battleships, bigger than the Nagato-class. However, she was cancelled due to the terms of the Washington Naval Treaty, and remodelled into an aircraft carrier to get around the terms of the treaty.
2. Shoukaku's historically known as the unlucky ship when paired with Zuikaku. In all the times they've sortied together, Shoukaku's always taken the brunt of the damage, requiring lengthy repairs back in Japan.
3. In-game, carriers are prevented from launching attacks when they receive moderate damage (chuuha). This can be a real godsend if an enemy carrier is hit before it gets its attack off. The exception to this are armoured aircraft carriers, which can still attack while moderately damaged.
4. In-game, it's common for players to hold off on using instant repair buckets whenever a major event is coming up. While they're not too hard to acquire, one can never have enough buckets, especially when event maps frequently cause players to use up literally hundreds of buckets trying to complete the maps within the time limit.
5. Historical note: Operation MO was the operation to take Port Moresby. All the ships that Ooyodo mentioned historically participated in that operation. This led to the Battle of the Coral Sea, which saw Shouhou sunk and Shoukaku damaged.