The year the mission takes place determines the level of equipment available. Aircraft are present. If the sub is near the shore or a carrier, occasional patrol aircraft could cause a bad day at sea. Ships in an attacked convoy will change speeds and courses in an attempt to escape destruction. Damage a ship and its speed diminishes.
Radio is used to give reports and orders, including downed pilot locations for pickup.
Missions also include shore parties and minelaying. Many types of surface ships are featured, including battleships and carriers. This subsim sent so far as to include the sun and moon, even with changing phases. After slowing down from accelerated time, a detected convoy might be too far out of range to plan an attack, whereas if you had been running in real time, you could have easily made the attack. But overall, Sub Battle shined.