A children's science fiction short story collection from the 1980's

Question

I am trying to find a collection of science fiction short stories and artwork which was in my elementary school library back in the early 1980's, however it may have been published in the late 1970's. The stories I remember are:

1. A space battle where soldiers drop from orbit, play dead on a tank and use it to break into an enemy stronghold.
2. Two children who escape an underground city to find giant robots launching missiles into the desert so humans think war is still occurring.
3. A survey team helping a primitive tribe destroy nests of "zwargs" or "Zargs".

There were a couple more stories but those are what I remember. It was a hardbound book with a yellow cover with science fiction artwork. The stories also had various science fiction illustrations.

Answer 1

Could it be Galactic Adventures?

One thousand of each type should suffice to clean out our Zwargs' nest for us. Half-an-hour later, Zebekee's preparations were ... Screeching with fury, the Zwargs fought ferociously as their stronghold was invaded on all four sides. .. [from Google Books]

The Google Books page has little bibliographic info (a 1980 pubdate and a partial table of contents). The ISFDB page says it was published by Rand McNally in 1980 (and has a different cover). Purnell apparently published the same book as Purnell's Book of Adventures in Space and the ISFDB entry is complete there.

The three stories are, respectively, "The Null-gravity Beam" by William Hall, "The Children" by Malcolm Hulke, and "Return of the Warriors" by John Grant.