[corsair15]

Air Patrols are unavoidable. You'll run into them everywhere, and they are the most dangerous threat to you. You can alleviate their pressure a bit though. Typical air patrol ranges were about 450 to 500 nautical miles (from smaller bases that have more fighters than long range aircraft). Also, an air patrol will never travel more than half the distance of it's ferry range (maximum range, traveling one-way). Here's what I do:

I go to the map (F3) and start drawing radius circles from all major and minor ports that are in Japanese control. Smaller bases such as (Wake Island, Majuro, Rabaul, etc.) will typically scramble fighter patrols more often than long range aircraft. So I draw a radius circle (Radius Circle Tool) 500nm from those bases, simply because an A6M2-5 Zero has a ferry range of about 1000nm. Therefore, it cannot travel further than 500nm and make it back to base; and I wouldn't expect an air-patrol further than that. I draw radius circles about 1000nm from major ports. So, now that you have your circles drawn, your next decisions depend on a couple of things.

What type of mission are you on? What realism level are you playing at? Do you play "Dead-is-dead?"

I play dead-is-dead all the time. If my sub sinks, I delete the file and start a new campaign. That affects my decisions. So here are some guidelines I use that you might consider.

If I'm on Photo-Recon missions, or Agent insertion missions, I play differently than when I'm on normal patrol.
Try this:

• If you pick up Radar Contacts, you should Crash Dive immediately. Make sure you are below 100 feet. Any less, and you're visible from the surface, and therefore an easy target.
• After crash diving, decrease speed to Ahead 1/3 and go to the Sonar Station to check for surface contacts. If you find a surface contact on the same bearing as your radar contact, you probably only picked up a naval vessel. Come back to periscope depth and check the bearing for aircraft. You should wait 5 minutes after checking before surfacing (It typically takes 4 and a half minutes after picking up radar contacts before they pass nearby.) If you see nothing, surface and continue with your mission or follow the ship if it's a surface contact.
• If the contact is behind you (Between 135 Degrees and 225 Degrees), you should still keep your speed at Ahead 1/3, but turn 90 Degrees to Port or Starboard and check the sonar again before coming back to periscope depth and repeating step 2.
• If you spot an aircraft while you are surfaced(sometimes you don't pick them up on radar), you have two options; fight it out and dive after the first attack, or crash drive immediately and go down to maximum operating depth at flank speed. If you spot it at periscope depth, dive immediately (Preferably below 200 Feet just in-case you still get spotted). Return to your original course, increase speed to Ahead 2/3. Wait an hour (time-compress it) and come back to periscope depth, check the sky again, wait 5 minutes; if there's nothing, surface and continue with your mission. I've noticed that it normally takes 45 minutes for the plane to pass by you again on it's return course, but I still wait an hour anyway.
• If you're getting buzzed by aircraft more than 4 or 5 times in a two or three hour period, there's probably a carrier nearby. I'll leave it up to you to decide what to do about that one.
• If you're inserting into enemy ports, or if you're nearby enemy held territories, you should expect to be buzzed constantly. You should run below 100 feet if possible at about (2 Knots). You can stay at this speed for days without running out of power.
• When recharging batteries in enemy territory, you should find a corner to hide in (or somewhere where patrols won't come by) and surface (preferably at night) at a full stop. Wait until recharged, submerge and continue on. If recharging while on patrol or in the middle of large areas of ocean. Recharge at Ahead 1/3 to recharge faster, but under no circumstances should the submarine stop.
• In the Early stages of the war (December of 41 to about June of 43) if you pick up Radar contacts at night, they'll almost always be surface contacts. After that, you'll start running into air-patrols at night as well, but even at the early stages of the war, I'd make it a habit to crash-dive anyway. Check the sonar, and decide what to do next.
• If you sustain any damage to your propulsion system, hull, or weapons system, return to port. Even if the damage is only 1 percent. Your maximum depth is decreased, and so is your range, and combat effectiveness. Just 1 percent might be the difference between surviving and dying. If you sustain damage in enemy territory, be prepared to give them everything you have (you might die anyway)
• If you run into destroyers or subchasers, go to maximum operating depth immediately. Decrease speed to less than 2.5 Knots, and pray. If the escorts get very close to the submarine, as their prop noises get louder, increase your speed. If they're right on top of you, increase to flank. When they start leaving you, decrease speed again.

Stick to those guidelines, and you should survive the entire war. Don't be conservative with the maximum depth of your submarine. I take mine there constantly, and I haven't died yet. It's about 328 feet. I always take mine to 325. Leave nothing to chance. One time I crash dived after spotting an A6M2 Zero about 100 miles west of Midway, at about 225 feet, the unthinkable happened. He hit his mark perfectly, and my submarine was smashed. Nearly 50 percent damage from one strike. Batteries were damaged, Deck Gun damaged, AA Gun sustained some damage but still worked (I had to surface and shoot him down), radar destroyed, control room and bow torpedo room flooding. I limped back to midway, and limped back to pearl right after that. There was no way I could finish the mission. Had I dove to 325, I may have evaded the attack. So don't be conservative with the uses of your submarine. Take it as far as it will go everytime. And plan EVERYTHING.

To answer your question. Running submerged all day while in the middle of the Pacific isn't entirely necessary. You can emerge an hour later and you probably won't run into another contact for a couple of hours. Running submerged all day near enemy territories is entirely necessary. You shouldn't risk running on the surface until nightfall. Like I said, 2 Knots and you should be able to run all day.

As for the U-Boat Add-on. I don't have it, but I do have an answer for you. There were nearly 1,000 U-Boats and only 250 U.S. Submarines, so it isn't surprising that U-Boat tonnages would be higher. There's more submarines, and therefore, more Contact reports. Giving more chances for submarines to attack convoys (Especially the big ones) It only makes sense for U-Boat Captains to have more tonnage on average. They get more reports.

Hope I helped and remember, leave nothing to chance; plan everything.

Thanks for reading,
Corsair15