Dwarfing a Federation Miranda-class starship and even the Earth Spacedock, the Whale Probe was cylindrical in shape, and carried a small deployable sphere normally stowed internally at the front, physically detached from the Probe while in use, but connected by an energy beam. The sphere's purpose was as a communication device, amplifying the Probe's broadcast of its calls to enormous levels, impacting on power systems and ecospheres. In comparison with the spacedock it passed at rather close range, the Whale Probe's estimated length was in the vicinity of seventy kilometers – one of the largest space vessels ever encountered by Starfleet, and potentially second only to V'Ger in size.
First Contact with the probe by a Federation starship was made by the USS Saratoga while patrolling the Neutral Zone. The Saratoga was disabled by the probe's powerful communication, as were at least seven other vessels along the probe's route to Earth, including the starships USS Yorktown and USS Shepard, and two Klingon vessels.
After disabling Spacedock and the prototype USS Excelsior, the Probe settled over the planet, directing its communications attempts towards its oceans. When it received no response, the Probe began vaporizing Earth's oceans, creating an impenetrable cloud cover over the planet, causing surface temperatures to plummet rapidly. The Federation President was forced to send out a planetary distress signal, which was picked up by Admiral Kirk, aboard the "HMS Bounty", a captured Klingon Bird-of-Prey. Spock, also aboard, quickly established that the probe's call was intended for the extinct cetacean species of humpback whale; Spock theorized that some other species had once been in contact with whales, and had sent the probe after the species went extinct to find out why they had lost contact.
Since destroying the probe wasn't possible, and they would be unable to communicate with the probe itself due to their ignorance of the whale "language", even if they could duplicate the sounds, Kirk determined that the only way to stop the probe was to find some humpbacks who could answer it. Consequently, the Bounty was taken into the past via the slingshot effect, and successfully retrieved two of the species from 1986. Returning to Earth, the two whales were able to respond to the probe's call, and it departed for an unknown destination, restoring power to the vessels it disabled along the way. (Star Trek IV: The Voyage Home)
Remarkable enough, a probe, cylindrical in nature was already envisioned in the reference work: Star Trek Spaceflight Chronology (p. 121) of 1979 as "first evidence of extra-galactic civilizations". In it, it was described as a small probe of unknown origin, measuring 2.0×0.375 meters. Nevertheless, it has been highly unlikely to have been the original inspiration for the eventual "Whale Probe".
Described in the script of Star Trek IV: The Voyage Home as "a simple cylinder, non-threatening but huge in size, with odd, eye-like antennae"', no specifics of the Whale Probe were ever given on screen. Yet, Effects Director of Photography Don Dow stated that as far as in-universe dimensions were concerned, "it was to be five miles long and a mile-and-a-half wide". (Cinefex, issue 29, p. 5)
The Whale Probe was designed by Nilo Rodis-Jamero, incorporating ideas he had received from The Film-Makers' Cooperative in Los Angeles, that translated into an apparently simple vaguely whale-like cylinder, transferred onto pre-production story-boards. (Cinefex, issue 29, p. 5)
Deceptively simple as it might had seemed, Industrial Light & Magic did encounter its share of problems during its efforts to realistically bring the concept of the probe onto the big screen. Model Shop Supervisor Jeff Mann recalled, "There were some difficulties early on with the probe, trying to get that to have some scale was difficult because it was big and shiny, it had blue-spill problems, early on we did a bunch of test to try to figure out what kind of texture or what we could do to give it that kind of scale that the starships had." (Star Trek IV: The Voyage Home (Special Edition), "From Outer Space to the Ocean"–special feature, disc 2) Dow elaborated, "I think the probe was the most difficult thing we had to work with on this show, simply because there was nothing to it. Our original instructions from L.A. were to make it "menacing, military and massive" and it was supposed to be about five miles long and a mile-and-a-half wide. To really do that, we would have had to build a model that was as big as a building. And because it was so devoid of detail, I was afraid it was just going to look like a giant water heater in space." (Cinefex, issue 29, p. 5)
Though starship-wise, the fourth feature was supposed to be light on ILM where starship studio models were concerned, no less than three models of the Whale Probe were constructed in the end. Mann recalled, "Since Nilo's concept was that the probe looked similar to a whale, we built a prototype that was a cylinder shape with barnacles and whale-like coloring–but still basically just a tube. We capped the ends of a piece of irrigation pipe and installed a mechanism to turn the ball-like antenna that jutted out from the bottom." (Cinefex, issue 29, p. 5)
Eventually the bullet was bitten and a model was constructed that according to Mann, "Basically, it's a cylinder that started off to look like a section of a whale. We used a barnacle type of texture for it, and it was originally painted with a crusty-textured white on a blue background. It was sort of organic looking, and that was the design we originally settled on. We built several versions of this monolithic probe that threatens the Earth. The main model we used was an eight foot long cylinder about two feet in diameter, and it had a hole at one end through which an antenna ball emerges on a shaft of light and sort of searches around." (American Cinematographer, October 1982, p. 68) Also constructed were a "smaller version to scale for the distance shots, and then we built a large section of the ship–just a third of the side of it –and it was tapered for a shot where the ship is heading towards camera and then flies overhead. Like a takeoff on that first shot in Star Wars. We also built some large antennas for close-ups.", as reported by Mann. (American Cinematographer, October 1982, p. 68) More specifically to the point Mann stated, "Our primary probe was eight feet long, but we also made a small one for the long-distance shots and another big section that was a forced perspective model–about twenty feet long and really wide at one end and the tapered back at the other." (Cinefex, issue 29, p. 5)
In order to save as much costs as post-production opticals were concerned, Mann decided to have his new Whale Probe models as much as possible have self-illuminating capabilities. Mann elaborated, "The Probe had a hole on the bottom that the ball jutted out from. Inside it, we put six halogen bulbs that emitted a general glow down onto the ball and out thew hole. Then, down the center we had a tube of plexiglass that was about two inches in diameter that attached to the ball. Inside of that was a long tube lamp–like a refrigerator lamp–which was just screwed into a 110 socket. So the stage crew could do several light passes on the probe." (Cinefex, issue 29, p. 5)
The whale-colored probe did not quite work out on screen, and after several shoots, a decision was made to alter the color scheme of the model as was recalled by Dow, "We had to give it some texture. After brainstorming it for a while, Ken Ralston came up with the idea of painting it shiny black and then backlighting it so there would be reflections coming off of it. We also ended up pock-marking the surface a little so that the backlighting would pick up some hills and valleys. Then we shot it with fog filters which helped to give it an awesome, mysterious quality." (Cinefex, issue 29, p. 6) Mann gave an additional reason from a different point of view, "We worked for quite a while on these models with a specific color and texture on mind, but then we reached a point where they just didn't look right. It wasn't exciting, because it was blue, like a whale. Also, the antenna originally didn't move and it didn't have a light source in it, so we made the antenna move and added an interior light to the ball. For the antenna's beam of light, we added a hot shaft of light in the center and put a much milder glow around that. I think it was Ken Ralston who came up with the idea to paint the probe black and eliminate all the color from it so we could use light and reflections on it to create interest and mystery." (American Cinematographer, October 1982, p. 68)
No matter what the original intent was, lighting the ball-shaped antenna presented its own set of additional problems as ILM's Optical Supervisor Ralph Gordon recalled, "The spherical antenna underneath the probe was originally shot so that it was orange., which unfortunately made it look very much like a spinning basketball. So we pulled mattes off of that that one element to drop it out–the ball itself had been shot separately from the probe–and then we made high-con elements that allowed us to expose blue light over that same area. We threw in all sorts of diffusion and filters on it to break up the image and give it a glow that looked like it was coming from the inside. That took a lot of finagling. We put diffusions on both the main projector head of our optical printer and on the aerial head, the back projector. We'd find a diffusion that worked somewhere, lock that off and then move the back head around trying to figure out where the best placement of the diffusion was. Like always, it was just a matter of trial and error." (Cinefex, issue 29, p. 6)
A sequel novel to Star Trek IV, Probe, accounted another run-in with the Probe during a proposed peace talk/joint archeology survey with the Romulans. Kirk and his crew later discover that the Probe was created by beings that resembled earth cetaceans and that it was damaged by what it described as "mites" in a cube shaped vessel which implies that it encountered the Borg before coming to Earth.
In the Myriad Universes novels, in an alternate timeline with both Kirk and Spock dead, the probe did indeed decimate Earth, leading Doctor Carol Marcus to attempt to use the Genesis Device to fix it.