Zond 5 carried the first terrestrial organisms to the vicinity of the Moon, including two Russian tortoises, fruit fly eggs, and plants.

[5] The tortoises underwent biological changes during the flight, but it was concluded that the changes were primarily due to starvation and that they were little affected by space travel.

It was launched by a Proton-K carrier rocket with a Block D upper-stage to conduct scientific studies during its lunar flyby.

[10] Two Russian tortoises (Agrionemys horsfieldii) were included in the biological payload, weighing 0.34–0.4 kilograms (0.75–0.88 lb) each pre-flight.

[15] However, the test subjects were not analogous to humans, because the choice of life forms were all extremophiles with a substantially higher radioresistance.

[16][17][18] The Russian Academy of Sciences stated that a mannequin equipped with radiation sensors occupied the pilot's seat.

[13] Mission Control discovered a problem with Zond 5's attitude and traced the cause to a contaminated star tracker.

[22] Eight ships were deployed to the Indian Ocean prior to launch, as a precaution in case the spacecraft could not reach Soviet territory; only three of them had rescue helicopters on board.

[23] The primary landing zone was in Kazakhstan, but instead Zond 5 splashed down in the Indian Ocean and was recovered by the Soviet vessels Borovichy (Боровичи) and Vasiliy Golovnin (Василий Головнин).

The sources indicated that the spacecraft landed in the Indian Ocean when the planned location was in Soviet territory, which was a factor in the recovery taking ten hours.

[32] The official Soviet news agency, TASS, announced in November 1968 that the flight carried living animals.

Another analysis showed the flying tortoises had elevated iron and glycogen levels in their liver and that the flight also affected the internal structures of their spleens.

The Soviets made this announcement a month before the planned Apollo 8 flight, in an attempt to show they were close to being able to carry out a crewed trip to the Moon.

[35][36] The Zond 5 caused a scare in the United States when on 19 September 1968, the voices of cosmonauts Valery Bykovsky, Vitaly Sevastyanov and Pavel Popovich were transmitted from the spacecraft and intercepted by Jodrell Bank Observatory and the CIA.

So I took the mic and said: "The flight is proceeding according to normal; we’re approaching the surface..." Seconds later my report – as if from outer space – was received on Earth, including [by] the Americans.

The U.S. space advisor Frank Borman got a phone call from President Nixon [actually Johnson], who asked: 'Why is Popovich reporting from the moon?'