Shahed-136One Way Attack Uncrewed Air Vehicle (), Source: Covert Shores
Covert Shores makes some interesting observations and asks pointed questions particularly in regard to the terminal homing phase of how the low-cost slow cruise missiles make their attacks on moving targets.
Hitting fixed target in Ukraine is very different from hitting a moving target hundreds of miles off the coast. Even an oil tanker is very small in the vastness of the ocean. The mission would need target location intelligence, and the drone would need targeting during its attack phase. The former is the same for any anti-ship weapon and can be achieved by patrol aircraft, fishing boats. Or, as possibly the case in the Chem Pluto attack, by the target broadcasting its position via AIS (automated information system).
The final phase targeting is more interesting. We do not know, at least in the public sphere, how the drones targeted the tankers. Whether it was a human-in-the-loop camera, or some form of automation.
Do they have satellite communications? Target recognition software? Home on AIS?
Presumably we have recovered at least one of the failed drones and can answer the question, but there is an even simpler solution.
Forward observers in one or more of the many Dhows that traffic the area, who call in a UAV when they have a target, and who can take over control of the drone when it arrives on scene, steering it into the target. This would be a continuation of what we saw with the Houthi remote control explosive motorboats, which unlike the USVs we are seeing in the Russo-Ukraine War, had no satellite link and were apparently steered by a second vessel within line of sight of the target and the attacking USV. It is not unlikely the Iranians and Houthi have a network of such nondescript vessels.
The slow speed of the UAVs does present something of a challenge in getting to the right place at the right time, but that is mitigated by the predictability of shipping lanes and the consistent speed of merchant vessels.
Chuck Hill's CG Blog 
Crashed ones have had mobile phone technology within them.
I strongly doubt it is using AIS in the terminal phase. First, many ships targeted were not broadcasting AIS. Second, the sophistication to use AIS to differentiate targets would significantly increase the expense, and these are low-cost weapons. Third, if they did use such sophistication, the hits would be located near the AIS antenna with some consistency — not exactly a location good for sinking or disabling a ship.
With the presence of three Iranian ships in the lower Red Sea, it seems to me a man-in-the-loop system using TV/IR is the most logical. TV/IR is a very mature (reliable) and prolific (hence cheap) system. My number 1 suspect would be MV Beshad, since it is an ISR-command vessel. Putting personnel on Houthi Dhows is also extremely likely.
MV Beshad (ISR), IRIS Bushehr (UnRep), and IRIS Alborz (frigate) are most-likely used to visually identify all ships in the target zone, so lack of AIS is meaningless. These vessels probably transmit to a higher HQ in Iran, where ships registries were checked for destination and ownership information and targets selected for transmission to the Houthis. And while the Houthis are supporting the attacks, it is highly likely Iranian “advisors” are on the ground in Yemen “helping.”
One of the lessons I hear no one talk about is the use of ballistic missiles and how they fail 100% without intervention of defensive measures. Few supersonic missiles have the ability for terminal-phase maneuvering (and these targets in the Red Sea are big and slow!), which means ballistic AShMs must have very, very long range sensors and targeting ability. – This makes the China threat less menacing in my mind.