At the beginning – tricky question :)

What is the most important unit in Homeworld online during skirmishes ? Battlecruiser certainly not!

The most important unit IS scout/probe !
Why ?

Homeworld game is based on rock-scissors-paper mechanics of gameplay. The most important is to KNOW what your enemy is doing.

1. How to spy with scout.

One of the first units you should build at the beginning is scout. Scout gives you ability to find out enemy positions and spy them to find out what they are doing.
Scout gives you also adventage in eliminating enemy probes in early stage.
At the beginning of the match build 1-2 scouts and send them to spy on enemy base. Place him far above or far below of the main planar scene. If you use him correctly, you can at the very edge of his field of view locate enemy capital ships and spy what they are doing. Scout has wider field of view then most of enemy units so you can spy without detection.
Of course you need to watch over your scouts because enemy can locate them and eliminate.

2. Scouting with “vanilla” probe.

Probes are quite good in spying but mostly I use them to secure flanks. I place them in regions where my ships could be outflanked to find out if nobody want to surprise me. I don’t use regular probes to spy on enemy`s “base” because they are easy to eliminate.
Also I probe distant asteroids fields to find out if enemy is not captured it and doing nasty things with resources ;)
If you do not have any spying unit in enemy “base” you can send one probe and watch what it will reveal before will be shoot down by enemy vessels.

Probes should be send up or down from main planar plane to increase chance of not being detected

3. Scounting with DOSTORTION probe.

This is my favourite! It is expensive (500 RUs to research) and few more to build BUT they are hard to detect. Enemy can detect them only in close proximity or using anti-distortion probes or sensors. Generally enemy do not know that near his base there is distortion probe placed and had no idea that they are being spied most of the time.

Probes should be send up or down from main planar plane to increase chance of not being detected

REMMEMBER! Probing and spying is the most important thing in homeworld online skirmishes.
You can counter enemy ships build up if you know what enemy is doing ! If you are able to spy on enemy most of time then you have HUGE advantage.

Thank you for reading and good luck! Follow me to learn many important aspects of online skirmishes.