Kind: captions
Language: en
This is a model of the first combat
submarine. Now, I say model because the
original doesn't exist. All we have is a
few hints and clues from subsequent
writings. The writings come from
American inventor David
Bushnull. The external shape of the
submarine vessel bore some resemblance
to two upper tortoise shells of equal
size joined together.
It was later nicknamed the
turtle. First, you've got the overall
shape. It's using the technology of a
barrel. It's thick oak staves bound
together with iron
hoops. It's not quite barrel shaped,
though. And the reason for that is
because you need space inside for an
operator to sit. So, that's going to
broaden it in the middle. And you need
space at the top for a hatch for the
operator to get
in. At first glance, it immediately
reminds you of a space capsule. But what
it is, in fact, is a time capsule. A
time capsule of contemporary
technologies. You've got these pedals
here. So, the operator is pedling away.
This is powered by pedal power. And they
are driving a propeller.
The concept of the propeller dates back
to Greek mathematician
Archimedes. His Archimedes screw
famously moved water using a spiral
blade inside a
tube. Bushnull took this concept and
located a blade on the outside of his
turtle. This is thought to be one of the
first practical applications of a
propeller. Along with a rudder, the
turtle has all the components needed to
maneuver on the
surface. A particular feature of the
outside of the vessel is this hatch at
the top here. It's got these watertight
windows. So, he has got some natural
light
inside. Then above there, these strange
looking things are really snorkel. so
that when it's above water, it's fully
ventilated.
Using the windows, the operator could
maneuver on the surface to locate and
position the turtle next to a
ship. It is then ready to
descend by filling the area at the base
of the vessel known as the
BGES. To do that, the operator kicks a
lever. This will flood the bes down
there with water. Under the surface, a
second propeller is used to lower or
raise the
turtle. Once submerged in darkness, the
operator has only two instruments for
guidance. This is a barometer. It has a
little cork in it, and each of these
marks on the glass tube represents a
fathom. That's about 6 ft. So, as he
sees the cork bobbing down, he knows
he's going down another 6 ft. How can he
see that underwater? Because it's been
covered with a fungus called fox fire,
which is luminous. It glows in the dark.
And over here is a compass, which again,
the needle on the compass has been
coated with this luminous fungus so he
can read his heading.
The turtle is designed to move into
position armed with a bomb to blow up
its target. So assuming that we've now
got to the right depth, we now need to
attach the payload. And that's this
crank here. This crank operates that
drill at the top. And that bs its way up
into the hull of a ship. The drill is
attached to the bomb by a rope. Once
connected, the turtle detaches itself,
leaving the explosive secured to the
ship. And now you've got to get out of
here. So you you pedal away. When you
want to surface, you use these two hand
pumps. Yet more exertion to save your
life, pumping away to get that water out
of the bes. But my goodness, that's a
heck of a lot of work to get to that
stage.
employed to carry out this dangerous
mission. 27-year-old American Ezra Lee.
The plan, drive into New York Harbor and
blow up the British flagship HMS
Eagle. But how could Ezra Lee attach a
bomb big enough to sink the British ship
and get away
safely? Inventor David Bushnell's
writings provide some clues.
allowing pyrochnics expert John
Hargreaves to figure out how it was
supposed to happen.
I've rigged this as a demonstration.
This is pretty much the size of the bomb
that would have been on the turtle that
holds the gunpowder. Correct. £150.
How do we get a spark to it? Well, in
the references to Bushnull's machine,
they show a flint lock mechanism. So,
this little pocket pistol, correct?
which has got this flint lock here. So
that
flint strikes that which creates the
spark.
The pistol's muzzle is screwed into the
barrel. When it's fired, it will ignite
the
gunpowder, but Ezra Lee would need time
to escape before it
exploded. Bushnull had a
plan. Within the magazine was an
apparatus constructed to run any
proposed length of time under 12 hours.
[Music]
This is a specialist clock. It is a very
early 19th century version actually, but
it's the nearest thing I could find to
the right mechanism. The mechanism John
thinks Bushnell used comes from a period
pocket watch. The pocket watch had been
around at the beginning of the 17th
century. It was a pretty rare thing and
they were all watches like
this. The clock is going to countd down
to zero. When it gets to zero, it pulls
a lever which I have attached to the
trigger mechanism of my pistol. So, it
pulls the trigger and fires the gun.
This is absolutely ingenious, John. I'm
going to set it to minute
two. Can you hear it ticking? We have a
ticking bomb. Yeah, this is ticking.
Woo! Look at that.
Excellent. Proof of concept. Yes.
The timer for the bomb was set to 30
minutes and sealed in a watertight
casing. The countdown would begin when
the bomb detached from the turtle.
[Music]
This apparatus could not possibly move
till by casting off the magazine from
the vessel. It was set in
[Music]
motion. The firing mechanism works on
land. But will the bomb explode
underwater? When Bushnull first tested
the bomb, he did so with varying amounts
of gunpowder.
For safety, Jon is only using five
pounds. Ezra Lee was carrying
150. At 11 p.m. on September 6th,
1776, after being launched into the
water from a whaleboat, Lee starts his
mission.
Even though this is a scaledown test,
Jon is taking all the necessary
precautions. Ezra Lee is facing the real
risk that the bomb could fail to
detonate or worse, explode too early,
killing him
instantly. For over two exhausting
hours, with the constant risk of being
spotted, he navigates toward the British
ship.
Upon reaching it, he begins his descent,
dropping close to 30 ft below the
surface with the
bomb. There she blows.
That's just £5. Yes, £5 of gunpowder.
The bomb they're dealing with was 30
times that magnitude.
A detonation that large would have been
catastrophic. The wooden hull of a ship
offers less resistance to the bomb's
explosive force than the denser water
around
it. It would have just ripped through
the bottom of the boat. Instant
destruction. Yeah.
But HMS Eagle is not blown
up. After making his descent, Ezra Lee
is unable to attach the
bomb. He went under the ship and
attempted to fix the wood screw, but
struck, as he supposes, a bar of
iron. At this crucial moment, running
out of air, he abandons the mission.
In a later attempt, the boat carrying
the sub is sunk by British
gunfire. This is the end of the turtle.
I have absolutely no doubt that if it
had been successful and if it had been
repeatable to scale, if they built many
more turtles and they had destroyed the
British fleet, it would have shortened
the war by years. The war would have
been over in months.