How does a steaming armada avoid submarine attack?

How can a big surface force, steaming more than a thousand miles towards a big mission, avoid enemy submarines? Like what the US carriers at Midway avoided, where Kurita failed in the first engagement at Leyte Gulf, where the Wasp and North Carolina failed at Guadalcanal, where Mikawa succeeded going in at Savo but failed in going out.

1. Are you still at risk of a torpedo attack when you're doing 30+ knots in open sea?
2. Can't you make occasional detours to throw off subs, search planes, and coast watchers?
3. The Atlantic war made me think it's the subs that are being hunted.

 

Destroyers, capable crews, well trained with top notch commanders. Some fish may still sneak through. Radio relay, “fish in the water”!

 

The Japanese submarines were older ones, and took longer to get on station. As such, the US carriers crossed the position a good 24-48 hours before the submarines arrived.

The US had ULTRA, and from these decrypts, we knew where Japanese shipping was going to be - this helped greatly to put US submarines in the paths of Japanese ships, but did not guarantee success. Also, Japanese ASW equipment and tactics tended to be lacking.

Early in the war US ASW gear and tactics were Also found to be wanting, hence the Japanese submarines scored several notable successes against US warships. Longer ranged torpedoes also helped, as they allowed Japanese subs to take shots beyond the US ASW screen. The North Carolina & O'Brien were also dumb luck , as those torpedoes missed their intended target and travelled some distance before hitting unintended targets.

Mikawa only had one destroyer with him at the time. They literally ran over S-38 on the way in - S-38 detected them to close to fire torpedoes. But, the Japanese were not as lucky on the way home, as S-44 was in an optimum spot to sink Kako.

Your always at risk...A high speed will help to minimize the risk(makes targeting calculations more difficult, reaction time will be reduced, and time in a torpedo danger zone will be lessened, etc.). But, there is always a risk.

Detours can be made, but this is mostly to keep the enemy guessing as to your destination or intentions.

To throw off a sub's aim, that would be called "Zig zagging." You have a base set course and then you zig 15 degrees to the left of the base course, hold that heading for a set number of minutes, then zag 15 degrees to the right of the base course and hold that for a set number of minutes. Wash, rinse, repeat. The problem with this is that you are just as likely to stumble into a submarine's crosshairs, as out of it. Another solution was continuous helming, where the ship is always slowly turning right or left - this is very strenuous on the ship's navigation team, but the submarine is faced with a constantly changing firing solution.

Subs were always hunter and hunted. IIRC, the US submarine service suffered the highest loss percentage of personnel, although the German submariners lost far more -upwards of 75% of the men.

In the Atlantic, the U-Boats tended to be the Hunters until about mid-1942, when the odds started to turn against them, the Allies had improved their radar, sonar, direction-finders, aircraft, and warships, as well as having refined their tactics, but the also added a large number of additional ASW escort vessels, and now had enough that they could form independent ASW Hunter-Killer groups specifically sent out to track down and sink German U-Boats.

 

#1 Big sea:small ships In the Atlantic and Arctic the convoys followed more or less set routes. If a line of u boats missed one convoy there would be another one.A lot of submarine success against warships was in restricted water.

#2 Much German success in finding convoys was attributed to the Germans breaking the British merchant codes,which helped to alert the u boats when and where to go.

#3 As has been pointed out warships travel faster.There was no successful interception of the larger liners used as troopships that sailed independently.

 

At the risk of stating the obvious, the ocean is a big place. One example, from Clay Blair's Hitler's U-Boat War: in 1939-41 the British ran approximately 900 convoys in the Atlantic. Only 291 ships were lost, the majority (187) from just 19 convoys losing 6-21 ships. About 90% of convoys were not even detected, let alone attacked.

We might phrase the question as how submarines do make contact. Usually there's some factor besides random chance. They may have information from codebreaking or other intelligence; this was a major factor in both the Atlantic and Pacific submarine campaigns. They may patrol around ports or choke points, although the enemy is likely to be aware of the danger. In the Guadalcanal example, the Japanese knew that American ships needed to support the Marines and supply convoys, even though the area became known as "Torpedo Alley". A side launching a major invasion could anticipate that the enemy fleet would respond and position subs to intercept, as at the Marianas and Leyte Gulf.

High speed was a considerable deterrent, though not infallible. Unless it happened to be right in the path of the target, a WWII submarine might not be able to get within range, especially submerged (both German and American subs had their best success when they were able to attack on the surface). They needed multiple observations to plot course and speed and develop a firing solution, and they would have less time to accomplish this against a fast target. Conversely, if the ship was steering a straight course and the sub had time to plot a solution, the actual speed didn't much matter, it was simple geometry.

 

The efforts of the USS England also illustrate how one could avoid submarine attacks on ones fleet.

 

Heavy destroyer/escort screen around the force should make it safer for the armada, but the threat is always present.

 

except for vessels like the Queen Mary, nobody did 30+ knots to transit. fuel consumption between 16 knots(a 'normal' transit speed) and 30 kts isn't double, it is about 5 times as much.
for subs, you zig-zag. sometimes random which makes it hard for a sub or a repeating pattern which makes it easier for the sub. for search planes, ships sometimes tried to stay in rain storms, worked against german and japanese aircraft, most did not have radar.
all subs were hunted. allies did a good job once radar and very long range aircraft with radar were added. in Pacific, US subs had more issues with friendly fire getting to patrol area than with japanese.