Here is the Google Ngram. A quick check shows that the effect holds up for "knots" as well. Although you do see things like this fairly often in earlier ngram years (small sample size) this seems unordinary for something as recent as 1943.
The peak is actually in 1944, which was the year that the Ashley Book of Knots (a pretty comprehensive encyclopedia describing thousands of knots) was published. It appears that this book is part of the data set that Google is using, and apparently its inclusion was enough to roughly triple the incidence of the word "knot" that year.