sonar
They used to train dolphins with cameras.
Sonar
It's called Sonar.
during World War 2
True
During World War II, U-boats could typically stay underwater for about 18-24 hours before needing to resurface to recharge their batteries and replenish their air supply.
Most likely Germany, they had the U-boats (underwater boats)
detector diodes in RADAR sets
trench was the most common but there was also airfighting and underwater in submarines ( then known as u boats)
for maram the angel to breathe underwater
Round with spikes
underwater submarine