** Archer Aviation's ACHR.N shares rise 20.6% to $5.36 on Mon after co and defense tech firm Anduril unveiled a co-developed autonomous aircraft platform

** ACHR stock bounces off 1-year low of $4.30 hit on Fri and on course for steepest one-day pct gain in over 14 months

** The platform is designed for commercial and military use; Anduril introduced the defense variant, Thunder, on Mon, with ACHR planning to unveil its commercial variant later this week

** Aircraft uses a hybrid-electric powertrain and is designed for missions including military strikes and cargo movement, allowing ACHR to expand beyond the urban air taxi market

** Even with the gain, ACHR stock down ~29% YTD and trading ~63% below 52-week intraday high of $14.62 hit on Oct 15

** Avg rating of 9 analysts covering the stock is "buy"; median PT $11.50, per LSEG data