IHW: Pigboats - Noises in the Deep

Speaking of Stress inducing events, depth charging is the main weapon of escorts against subs, and an utterly terrifying experience. A big part of the this is the sequence of auditory assaults the depth charging sets up on the crew.

First is the pinging, the active echolocation pulse emitted by SONAR. There were two types of pings used - long scale and short scale. Long scale pings were emitted when an escort suspected a sub was about, but not exactly where. They sounded something like this: Peee-eeep... Pee-eeep... Pee-eeep... as they searched for a contact below the waves. Short scale pings where higher pitched and came faster: PEEP! PEEP! PEEP! Hearing them meant the escort had a solid contact - most likely on your boat - and would soon be boring in for the kill.

Merchant ships almost always had a single screw - it just wasn't profitable for most to give up the space and mass a second boiler.engine and screw would need. The single screw sounded like this on the hydrophones: Thumpthumpthumpthump. If your boat was close, you could hear it through the water without the phones.

Escorts needed more speed, and economics wasn't really in the calculations, so they generally had dual screws. The slight asynchronization between the screws - no two screws are ever exactly in phase - created a phantom "beat" between them. When relaxed and going about their business, escorts had a sound like this: Shooshooshooshooshooshoo. When they got excited, as when they found a target for their depth charges, the pitch and tempo increased, getting louder as it came nearer, and dropping in pitch - Doppler effect - as it passed overhead and went away: ShumshumshumshumSHUMSHUMSHUMSHUMSHUMSHUMSHUMSHUMSHUMSHUMSHUMSHUMSHUMSHUMSHUMSHUMSUMESHUM SHUMSHUMSHUMSHUMSHUMSHUMSHUMSHUMshumshumshumshum.

You could sometimes hear the splashes made by the depth charges as they were dropped or shot to the sides. At any rate you could always hear the depth charges go off! Depth charges had a double actioned sound: click-WHAM! click-WHAM! click-WHAM! If they came fast and close together, the explosions cascaded into each other: click-WHAM! WHAM!WHAM-WHAM-WHAM! WHAM!

Torpedoes when they hit carried their own sound, different from a depth charge, sort of like hitting a boiler with a baseball bat: WHANGG! and WHANGG! And the sweetest underwater music of all were the breaking up noises made by a sinking ship - shrieks and groans and crashes and muffled whumps as the steel frame was tortured and twisted by the pressures of the deep.

-clash