[music] announcerer: coming up on "2121st century"."... worldwide nuclear monitoring, the last link in the chain. blinded in gaza, but not giving up on education. and refugees in japan. man's voice: 5, 4... [e[explosion] man: we had a mission to install that station. and despite the didifficulties, despite e the hh

environment, we had to do it. man: you start finally seeing data. so you start hearing hearing whales, you start-- you suddenly have e eyes underwater.. narrator: a 20-year journey is nearing its end. but for the comprehensive nuclear test ban treaty organization, which monitotors r entire planet for nuclear tests, the work is far from over. totoomplete its s capability too hearar nuclear explolosions inhe world's oceans, ctbto musust fit

install a a hydro-a-acoustic nitoring statation in one e of e most remote placeses on earth-- the ocean floor halfway between africa and antarctica. when completed, hydro-acoustic station number 4 at the crozet islands will l join thehe ctbto internatioional monitoring system toetetect and alert the e world ofof nuclear testing. jerry stanley: installing a hydro-acoustic station is a complex social engineering task. the hydro-acoustic system we're installing at crozet is s one of 6 hydydro-acoustic stations. but these hydro-acoustic stationons are part of thee international monitoring system, which has over 300 stations listening for potential nuclear tests aroround the globobe. manan: 10... narrator: we proceed to develop more accurate and dedestructive nuclear w weapons. over 2,000 nuclear bombs were detoted in

the lasast half of the 20thth century. [e[explosion] but in 1996, the global community said "enough" and signed the united nations comprehensive nuclear test ban treaty. today, 183 countries have voluntaririly agreed to stp nuclear testing. but while signed in good faith, the mission of the ctbto is to verify the treaty's compliance with hard data. stanley: we're moving towards the final stages now of installing the hao4 station, but we were working in the roaring forties, so the weather can be very unpredictable. mario zampolli: those places, the roaring forties, are legendary among sailors and people who work at sea as some as some of the most difficult oceans in the world. you have what is called an unlimited fetch,

currents that are also merging, coming down from south africa, merging with certain polar currents, that go all around the world, really undisturbed. in these difficult conditions was really something that p put a lot of streress on everybody, on all the tteams. you know that you'u're t afafforded, you'u're not allllod many mistakes. patrick grenard: of course it's not only a harsh environment above the sea surface, it's also a harsh environment underwater. but we knew that we had a mission to accomplish. it was to install that station despite the difficiculties, despe e the harsh environment, the complexity of the project, we had toto do it.

man: once we get going, we can adjust it, ok? narrator: after more than 4 years of meticulous planning, two triplets of underwater microphones called hydrophones are finally loaded onto a specialized cable ship. ststanley: we have to be very careful loading our system on. we have a lot of cables connecting the system together, and there's also some delicate electronics, the laser systems, eet cetera. we have specialist crane operators and 10 people-- 10 people-plus supporting the loading. man: [indistinct] stanley: and then we transit to the cable factory in port smith. narrator: it will take 3 days to load 120 kilometers of underwater cable...and another 5

weeks to reach the crozet islands in the south indian ocean. [man speaking french] [penguins squawking] [daniel fouquet speaking french]

[fouququet speaking french] zampolli: several experts advised us that a good time to be there would be between december and february. however, it turns out that december was jujust apppparentle of the worst ones they've ever had on record. man: whoa. zampolli: what was happening there was that there were these systems brewing up south of south africa and being launched by the winter waters like frisbees. freezingng cold hurriricanes, with snow, hail, and the windnd star t to be abobout more e tha0 miles an hour, you hahave to go down and walk on all fours and work your way up, because dinner r is up at the base. [laughs]

narrator: brief breaks betwtween passing storms allow just enough time to o deoy t the hrophphones to the sea floor. when all systems are e go, the ship releasases the orange floaoats m eir anchors, lifting the underwaterer microphones to ther intendeded depths. zampolli: and thenen... bang--you see these things arrive and then you start finally seeing data. you start hearing whales, you start... you suddenly have eyes underwater. narrator: from the indian ocean down to the arctic sea, from the atlantic to the pacific, hydro-acoustic station number 4 at the crozet islands is now online, relaying data in real time to ctbto h headquarterers n vienna. the data is analyzed and shared with its test ban treaty member ststates almost as fast as it comes in. with 90% of its entire

international monitoring system in plalace and its capability to monitor the world's oceans complete, the ctbto can detect and alert the world toto any potential nucleaear test anywhee on the planet, 24-7, 365 a year. [indistinct] [rumbling]

[beeping] [doctor speaking english] [leader speaking arabic] [girl crying] [speaking arabic] [second girl speaking arabic] [beeping]

[indidiinct conversation] [wooman speakiking english]

[mother speaking arabic] [leader speaking arabic] [girl speaking arabic]

[doctor speaking english]

[chatter, rhythmic clapping] [leader on loudspeaker]

[whistle blows] [leader speaking arabic]

[music playing] unrwa worker: as-salaam alaikum. class: wa-alaikum salaam.

[siren]

[woman speaking japanese]

er in foreign lalanguage] >> [breathing heavily] >> i was searchihing for an exit option from gaza for my palestinian family.